Filed Pursuant to Rule 424(b)(5)
Registration Statement No. 333-166514

PROSPECTUS SUPPLEMENT
(To prospectus dated May 26, 2010)

11,927,034 Shares of Common Stock
Warrants to Purchase 4,174,462 Shares of Common Stock

     We are offering directly to selected investors up to 11,927,034 shares of our common stock and warrants to purchase up to 4,174,462 shares of our common stock pursuant to this prospectus supplement and the accompanying prospectus. The common stock and warrants will be sold in units, with each unit consisting of one share of common stock and a warrant to purchase 0.35 of a share of common stock, at an initial exercise price of $1.755 per share. Each unit will be sold at a negotiated price of $1.35 per unit. We refer to the shares of common stock issued or issuable hereunder and the warrants to purchase common stock issued hereunder, collectively, as the securities. The shares of common stock issuable from time to time upon exercise of the warrants are also being offered pursuant to this prospectus supplement and the accompanying prospectus.

     Our common stock is listed on the NASDAQ Global Market under the trading symbol “ALXA.” On May 2, 2011, the last reported sales price for our common stock on the NASDAQ Global Market was $1.63 per share. There is no established public trading market for the offered warrants and we do not expect a market to develop. In addition, we do not intend to apply for listing of the warrants on any national securities exchange.

     INVESTING IN THE SECURITIES INVOLVES A HIGH DEGREE OF RISK. SEE THE SECTION ENTITLED “RISK FACTORS” BEGINNING ON PAGE S-10 OF THIS PROSPECTUS SUPPLEMENT AND IN OUR FILINGS WITH THE SECURITIES AND EXCHANGE COMMISSION, WHICH ARE INCORPORATED BY REFERENCE IN THIS PROSPECTUS, TO READ ABOUT FACTORS YOU SHOULD CONSIDER BEFORE BUYING OUR SECURITIES.

	Per Unit		Total(1)
Public offering price	$	1.35	$	16,101,496
Proceeds, before expenses, to us	$	1.35	$	16,101,496

(1) Assumes all units offered pursuant to this prospectus supplement are sold.

     We expect the total offering expenses to be approximately $250,000 for all sales pursuant to this prospectus supplement and accompanying prospectus. Because there is no minimum offering amount required as a condition to the closing of this offering, the actual public offering amount and proceeds to us are not presently determinable and may be substantially less than the maximum amounts set forth above. The closing of this offering is subject to certain conditions. We expect this transaction to close on or before May 6, 2011, and to deliver the securities to investors on or about May 6, 2011. The units will not be issued or certificated. The shares of common stock and warrants are immediately separable and will be issued separately.

     You should carefully read this prospectus supplement and the accompanying prospectus, together with the documents incorporated by reference, before you invest in the securities.

     NEITHER THE SECURITIES AND EXCHANGE COMMISSION NOR ANY STATE SECURITIES COMMISSION HAS APPROVED OR DISAPPROVED OF THESE SECURITIES OR PASSED UPON THE ACCURACY OR ADEQUACY OF THIS PROSPECTUS SUPPLEMENT OR THE ACCOMPANYING PROSPECTUS. ANY REPRESENTATION TO THE CONTRARY IS A CRIMINAL OFFENSE.

The date of this prospectus supplement is May 3, 2011.

TABLE OF CONTENTS

Prospectus Supplement

ABOUT THIS PROSPECTUS SUPPLEMENT	S-3
FORWARD-LOOKING INFORMATION	S-4
PROSPECTUS SUPPLEMENT SUMMARY	S-5
THE OFFERING	S-8
RISK FACTORS	S-10
USE OF PROCEEDS	S-11
CAPITALIZATION	S-12
DILUTION	S-13
PLAN OF DISTRIBUTION	S-14
DESCRIPTION OF COMMON STOCK	S-16
DESCRIPTION OF WARRANTS	S-16
LEGAL MATTERS	S-18
EXPERTS	S-18
WHERE YOU CAN FIND MORE INFORMATION	S-18
INCORPORATION BY REFERENCE	S-18
Prospectus
ABOUT THIS PROSPECTUS	2
OVERVIEW	3
RISK FACTORS	8
FORWARD-LOOKING INFORMATION	8
USE OF PROCEEDS	8
DESCRIPTION OF CAPITAL STOCK	9
DESCRIPTION OF DEBT SECURITIES	12
DESCRIPTION OF WARRANTS	18
DESCRIPTION OF UNITS	20
LEGAL OWNERSHIP OF SECURITIES	21
PLAN OF DISTRIBUTION	24
LEGAL MATTERS	27
EXPERTS	27
WHERE YOU CAN FIND MORE INFORMATION	27
INCORPORATION BY REFERENCE	27

     You should rely only on the information contained in or incorporated by reference into this prospectus supplement and the accompanying prospectus. We have not authorized any other person to provide you with information that is different from that contained in this prospectus supplement or the accompanying prospectus. If anyone provides you with different or inconsistent information, you should not rely on it. The information contained in or incorporated by reference into this prospectus supplement and the accompanying prospectus is current as of the date such information is presented, regardless of the time of delivery of this prospectus supplement or of any sale of the securities. Our business, financial condition, results of operations and prospects may have changed since those dates. This prospectus supplement supersedes the accompanying prospectus to the extent that it contains information that is different from or in addition to the information in the accompanying prospectus. You should read this prospectus supplement and the accompanying prospectus, including the documents incorporated by reference herein and therein, before making an investment decision. You should also read and consider the information in the documents we have referred you to in the section entitled “Where You Can Find More Information” and “Incorporation by Reference” below. You should consult with your own advisors as to the legal, tax, business, financial and related aspects of a purchase of the units.

S-2

ABOUT THIS PROSPECTUS SUPPLEMENT

     This prospectus supplement is a supplement to the accompanying prospectus, dated May 26, 2010, that is also a part of this document. This prospectus supplement and the accompanying prospectus are part of a registration statement on Form S-3 (File No. 333-166514) that we filed with the Securities and Exchange Commission, or the SEC, using the “shelf” registration process that was declared effective on May 20, 2010. Under this “shelf” registration process, we may from time to time sell any combination of securities described in the accompanying prospectus in one or more offerings up to a total of $75.0 million.

     This document is in two parts. The first part is this prospectus supplement, which describes the specific terms of the offering and also supplements, adds to and updates information contained in the accompanying prospectus and the documents incorporated by reference into the accompanying prospectus. The second part is the accompanying prospectus, which provides more general information, some of which may not apply to the securities. Generally, when we refer to this prospectus, we are referring to both parts of this document combined. To the extent there is a conflict between the information contained in this prospectus supplement, on the one hand, and the information contained in the accompanying prospectus or any document incorporated by reference therein, on the other hand, you should rely on the information in this prospectus supplement. If any statement in one of these documents is inconsistent with a statement in another document having a later date—for example, a document incorporated by reference in the accompanying prospectus—the statement in the document having the later date modifies or supersedes the earlier statement.

     This prospectus contains summaries of certain provisions contained in some of the documents described herein, but reference is made to the actual documents for complete information. All of the summaries are qualified in their entirety by the actual documents. Copies of some of the documents referred to herein have been filed, will be filed or will be incorporated by reference as exhibits to the registration statement of which this prospectus is a part, and you may obtain copies of those documents as described below under the section entitled “Where You Can Find Additional Information.”

     Unless stated otherwise, references in this prospectus supplement and the accompanying prospectus to “Alexza,” “we,” “us,” or “our” refer to Alexza Pharmaceuticals, Inc., a Delaware corporation, and its subsidiaries.

     The names “Alexza Pharmaceuticals,” “Alexza,” and “Staccato” are registered trademarks of Alexza Pharmaceuticals, Inc. All other trademarks, trade names and service marks appearing in this prospectus supplement and accompanying prospectus are the property of their respective owners.

     We are not making any representation to you regarding the legality of an investment in the securities by you under applicable law. We are not making an offer to sell the securities in any jurisdiction where the offer or sale is not permitted. Persons outside the United States who come into possession of this prospectus supplement and the accompanying prospectus must inform themselves about, and observe any restrictions relating to, the offering of the securities and the distribution of this prospectus supplement and the accompanying prospectus outside the United States.

S-3

FORWARD-LOOKING INFORMATION

     This prospectus supplement and the accompanying prospectus and the documents that we have filed with the SEC that are incorporated by reference herein and therein contain forward-looking statements within the meaning of Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended, that are subject to the “safe harbor” created by those sections. Examples of these statements include, but are not limited to, statements regarding the following: the prospects of us receiving approval to market AZ-004, our anticipated timing and prospects for the resubmission of our New Drug Application for AZ-004, management’s plans for the use of the net proceeds from the offering, the implications of interim or final results of our clinical trials, the progress and timing of our research programs, including clinical testing, the extent to which our issued and pending patents may protect our products and technology, the potential of our product candidates to lead to the development of safe or effective therapies, our ability to enter into collaborations, our future operating expenses, our future losses, our future expenditures and the sufficiency of our cash resources.

     These forward-looking statements are generally identified by words such as “may,” “will,” “could,” “would,” “should,” “expect,” “intend,” “plan,” “anticipate,” “believe,” “estimate,” “predict,” “project,” “potential,” “continue,” “ongoing” or the negative of these terms or other comparable terminology, although not all forward-looking statements contain these words. Discussions containing these forward-looking statements may be found, among other places, in “Business,” “Risk Factors” and “Management’s Discussion and Analysis of Financial Condition and Results of Operations” incorporated by reference from our most recent Annual Report on Form 10-K as well as any amendments thereto reflected in subsequent filings with the SEC. These forward-looking statements involve known and unknown risks, uncertainties and other factors that may cause our actual results, levels of activity, performance or achievements to be materially different from the information expressed or implied by these forward-looking statements. While we believe that we have a reasonable basis for each forward-looking statement contained in this prospectus supplement, we caution you that these statements are based on a combination of facts and factors currently known by us and our projections of the future, about which we cannot be certain. As a result of these factors, we cannot assure you that the forward-looking statements in this prospectus supplement and the accompanying prospectus or documents incorporated by reference will prove to be accurate. Furthermore, if our forward-looking statements prove to be inaccurate, the inaccuracy may be material. In light of the significant uncertainties in these forward-looking statements, you should not regard these statements as a representation or warranty by us or any other person that we will achieve our objectives and plans in any specified time frame, or at all. You should not place undue reliance on these forward-looking statements, which apply only as of the date of this prospectus supplement. You should read this prospectus supplement, the accompanying prospectus, the registration statement of which this prospectus supplement and the accompanying prospectus is a part and the documents incorporated by reference herein and therein completely and with the understanding that our actual future results may be materially different from what we expect.

     You should assume that information contained in or incorporated by reference into this prospectus supplement and the accompanying prospectus is accurate only as of the date on the front cover of this prospectus supplement, the accompanying prospectus or the date of the document incorporated by reference, as applicable. We undertake no obligation to publicly update any forward-looking statements, whether as a result of new information, future events or otherwise. You are advised, however, to consult any further disclosures we make on related subjects in our Annual Reports on Form 10-K, Quarterly Reports on Form 10-Q and Current Reports on Form 8-K, as well as any amendments thereto.

S-4

PROSPECTUS SUPPLEMENT SUMMARY

     This summary highlights selected information contained elsewhere or incorporated by reference in this prospectus supplement. This summary does not contain all the information that you should consider before investing in the securities. You should read the entire prospectus supplement and the accompanying prospectus carefully, including “Risk Factors,” the financial statements and other information included or incorporated by reference in this prospectus supplement and the accompanying prospectus before making an investment decision. This prospectus supplement contains forward-looking statements that involve risks and uncertainties. Our actual results could differ materially from the results anticipated in these forward-looking statements as a result of factors described under the “Risk Factors” section and elsewhere in this prospectus supplement and in the risk factors set forth under “Item 1A. Risk Factors” in our Annual Report on Form 10-K for the year ended December 31, 2010 and elsewhere in the documents incorporated by reference. All references in this prospectus supplement to “$” are to U.S. dollars.

Our Business and Technologies

     We are a pharmaceutical company focused on the research, development, and commercialization of novel proprietary products for the acute treatment of central nervous system conditions. All of our product candidates are based on our proprietary technology, the Staccato system. The Staccato system vaporizes an excipient-free drug to form a condensation aerosol that, when inhaled, allows for rapid systemic drug delivery. Because of the particle size of the aerosol, the drug is quickly absorbed through the deep lung into the bloodstream, providing speed of therapeutic onset that is comparable to intravenous, or IV, administration but with greater ease, patient comfort and convenience.

     In early 2010, we conducted a thorough review of our product pipeline, evaluating current and potential new Staccato-based product candidates. This review yielded three categories of Staccato-based product candidates: (1) product candidates where we believe we can add value through internal development, (2) product candidates where we have developed the product idea, but where a development partner is required, and (3) product candidates based on new ideas, primarily focused on new chemical entities, where the Staccato technology can facilitate better or more effective delivery. In July 2010, we announced that, in addition to AZ-004, AZ-007 (Staccato zaleplon) and Staccato nicotine would remain in active development. Active development on the remainder of our development pipeline is suspended. We are continuing to seek partners to support development and commercialization of our product candidates, and we believe that any potential partnership agreement for AZ-004 in the U.S. and Canada will have similar terms to those of our agreements with Biovail Laboratories International SRL, or Biovail, despite those agreements having been terminated.

     Our product candidates in active development are:

•

AZ-004 (Staccato loxapine). We are developing AZ-004 for the rapid treatment of agitation in patients with schizophrenia or bipolar disorder. In December 2009, we submitted a New Drug Application, or NDA, for AZ-004, submitted as AdasuveTM Staccato® (loxapine) inhalation aerosol, 5 mg and 10 mg. In October 2010, we received a Complete Response Letter, or CRL, from the U.S. Food and Drug Administration, or the FDA, regarding our NDA for AZ-004. A CRL is issued by the FDA indicating that the NDA review cycle is complete and the application is not ready for approval in its present form. In December 2010, we completed an End-of-Review meeting with the FDA to discuss the issues outlined in the AZ-004 CRL. In January 2011, we received the official FDA minutes of the meeting, and we anticipate resubmitting the AZ-004 NDA in July 2011. We are seeking commercial partners for the worldwide development and commercialization of AZ-004.

In the CRL, the FDA stated that its primary clinical safety concern was related to data from the three Phase 1 pulmonary safety studies with AZ-004. This concern was primarily based on observed, dose-related post-dose decreases in forced expiratory volume in one second, or FEV1, a standard measure of lung function, in healthy subjects and in subjects with asthma or chronic obstructive pulmonary disease, or COPD. The FDA also noted that decreases in FEV1 were recorded in subjects who were administered device-only, placebo versions of AZ-004. In the information package submitted to the FDA in response to the CRL and in preparation for the End-of-Review meeting, we presented evidence

S-5

	that we believe demonstrates that the placebo device is safe, including a blinded expert review of the flow-volume loops data from the healthy subject study as further evidence that there appears to be no consistent pattern suggestive of airway obstruction in these subjects. We also provided an analysis that we believe shows that there is no meaningful temporal relationship between placebo administration and decreases in FEV1. We believe this evidence and analysis confirm that the changes seen were likely background events in the population studied, where the repeated and extensive pulmonary function testing may have contributed to some of the observations. Additionally, we believe we showed that the aerosol characterization does not indicate a basis for concern. We agreed to reiterate these arguments in our NDA resubmission.
	In the information package, we also believe we showed that the pulmonary safety program in subjects with asthma or COPD had identified patients who may be susceptible to bronchospasm, the nature of this adverse event, and how it can be managed. We stated we believe the risk in these patients could be mitigated through labeling and a Risk Evaluation and Mitigation Strategy, or REMS, program. At the End-of-Review meeting, the FDA stated that it would be reasonable to propose a REMS program for the use of Staccato loxapine, and requested that as part of our resubmission, we provide a detailed REMS proposal including labeling, a medication guide and a communication plan, to manage the potential risks. In the resubmission, we must also show how to identify patients at risk of developing pulmonary side effects, as well as a way to decide who should and should not be treated with Staccato loxapine when they present for treatment. The FDA also informed us that it would likely present the NDA to an advisory committee.
	The CRL also raised issues relating to the suitability of our stability studies and certain other Chemistry, Manufacturing, and Controls, or CMC, concerns, including items relating to the FDA’s pre-approval manufacturing inspection. Because AZ-004 incorporates a novel delivery system, the CRL included input from the FDA’s Center for Devices and Radiological Health, or the CDRH. In the CRL, the CDRH requested a human factors study and related analysis to validate that the product can be used effectively in the proposed clinical setting. We have finalized the protocol with input from the FDA and expect to complete this study in the coming months. We are not currently required to conduct any additional efficacy or safety clinical trials for AZ-004. The CDRH also requested further bench testing of the product under an additional “worst-case” manufacturing scenario. We have completed this additional “worst-case” bench testing of the product, submitted the data to the FDA and believe that this issue has been adequately addressed.
	In February 2010, we entered into a collaboration and license agreement, or license agreement, and a manufacture and supply agreement, collectively, the collaboration, with Biovail for AZ-004 for the treatment of psychiatric and/or neurological indications and the symptoms associated with these indications, including the initial indication of treating agitation in schizophrenia and bipolar disorder patients. On September 27, 2010, Biovail and Valeant Pharmaceuticals International completed a merger. On October 18, 2010, Biovail notified us of its intention to terminate the collaboration. Upon the termination, we reacquired the United States and Canadian rights to AZ-004 and have worldwide rights. Neither Alexza nor Biovail incurred any early termination penalties in connection with the termination of the collaboration.
•	AZ-007 (Staccato zaleplon). We have completed Phase 1 testing for AZ-007. This product candidate is being developed for the treatment of insomnia in patients who have difficulty falling asleep, including patients who awake in the middle of the night and have difficulty falling back asleep. In the Phase 1 study, AZ-007 delivered an IV-like pharmacokinetic profile with a median time to peak drug concentration of 1.6 minutes. Pharmacodynamics, measured as sedation assessed on a 100 mm visual-analog scale, showed onset of effect as early as 2 minutes after dosing. We do not intend to spend any external development resources on AZ-007 in the first half of 2011, but are continuing internal work on the technical product development of AZ-007.
•	Staccato nicotine is designed to help smokers quit by addressing both the chemical and behavioral components of nicotine addiction by delivering nicotine replacement via inhalation. On August 25, 2010, we entered into a license and development agreement, or the Cypress Agreement, with Cypress

S-6

Bioscience, Inc., or Cypress, for Staccato nicotine. According to the terms of the Cypress Agreement, Cypress paid us a non-refundable upfront payment of $5 million to acquire the worldwide license for the Staccato nicotine technology. In addition, following the completion of certain preclinical and clinical milestones relating to the Staccato nicotine technology, if Cypress elects to continue the development of Staccato nicotine, Cypress is obligated to pay to us an additional technology transfer payment of $1 million. We have a carried interest of 10%, subject to adjustment in certain circumstances, in the net proceeds of any sale or license by Cypress of the Staccato nicotine assets and the carried interest will be subject to put and call rights in certain circumstances. Under the Cypress Agreement, Cypress has responsibility for preclinical, clinical and regulatory aspects of the development of Staccato nicotine, along with the commercialization of the product. As of April 30, 2011, Cypress has paid us the total $3.9 million for our efforts to execute a defined development plan for Cypress culminating with the delivery of clinical trial materials for a Phase 1 study with Staccato nicotine, as contemplated by the Cypress Agreement.

     Other than those licensed to Cypress, we currently retain all rights to our product candidates and the Staccato system. We intend to capitalize on our internal resources to develop certain of our product candidates and to identify routes to utilize external resources to develop and commercialize other product candidates.

     We were incorporated on December 19, 2000. We have funded our operations primarily through the sale of equity securities, payments received pursuant to collaborations, capital lease and equipment financings, debt financings and government grants. We have generated $59.8 million in revenues from inception through December 31, 2010, primarily through license and development agreements, United States Small Business Innovation Research grants and drug compound feasibility studies. Prior to 2007, we recognized governmental grant revenue and drug compound feasibility revenue. However, we expect no grant revenue or drug compound feasibility screening revenue in 2011. We do not expect any material product revenue until at least 2012.

     We have incurred significant losses since our inception. As of December 31, 2010, our deficit accumulated during development stage was $266.1 million and total stockholders’ equity was $12.3 million. We recognized net losses of $1.5 million, $56.1 million, $77.0 million in 2010, 2009 and 2008, respectively, and $311.2 million in the period from December 19, 2000 (inception) to December 31, 2010. In January 2009, we consolidated our operations to primarily focus our efforts on the continued rapid development of AZ-004. We expect our net losses to increase in 2011 compared to 2010, as the 2010 results were impacted by the $40 million of revenue recognized from the termination of our license agreement with Biovail for AZ-004.

General Information

     Our principal executive offices are located at 2091 Stierlin Court, Mountain View, CA 94043 and our telephone number is (650) 944-7000. Our website address is http://www.alexza.com. The information contained in, or that can be accessed through, our web site is not part of this prospectus supplement or the accompanying prospectus and should not be relied upon in connection with investing in the securities.

S-7

THE OFFERING

Common stock offered by us	11,927,034 shares
Warrants offered by us	Warrants to purchase up to 4,174,462 shares of our common stock. This prospectus supplement also relates to the offering of the shares of our common stock issuable upon exercise of the warrants.
Common stock outstanding before the offering	60,184,774 shares
Common stock outstanding after the offering	72,111,808 shares (assuming none of the warrants issued in this offering are exercised) (1)
Use of Proceeds	We currently anticipate that the net proceeds from the sale of the securities will be used primarily for general corporate purposes, including regulatory activity, clinical trial, research and development, general and administrative and manufacturing expenses. We may also use a portion of the net proceeds to acquire or invest in businesses, products and technologies that complement our business. See “Use of Proceeds” on page S-11.
Risk Factors	See “Risk Factors” beginning on page S-10 and in our most recent Annual Report on Form 10-K for a discussion of factors you should carefully consider before deciding to invest in the securities.
NASDAQ Global Market symbol	Our common stock is listed on the NASDAQ Global Market under the trading symbol “ALXA.” There is no established public trading market for the offered warrants and we do not expect a market to develop. In addition, we do not intend to apply for listing of the warrants on any national securities exchange.

(1)	The number of shares of common stock to be outstanding immediately after this offering as shown above is based on 60,184,774 shares of common stock outstanding on May 2, 2011.
	Unless we specifically state otherwise, the information throughout this prospectus supplement excludes, as of May 2, 2011:

• 3,134,460 shares of common stock issuable upon exercise of outstanding options granted under our equity incentive plans at a weighted average exercise price of $2.75 per share;

• 16,446,527 shares of common stock issuable upon exercise of warrants outstanding at a weighted average exercise price of $2.84 per share;

• 1,438,806 shares of common stock issuable upon the vesting of outstanding restricted stock units;

• 2,578,131 shares of common stock available for grant under our 2005 Equity Incentive Plan and 2005 Non-Employee Directors’ Stock Option Plan; and

• 59 shares of common stock available for sale under our 2005 Employee Stock Purchase Plan.

S-8

Ratio of Earnings to Fixed Charges

     Our earnings were insufficient to cover fixed charges in each of the years in the five-year period ended December 31, 2010. “Earnings” consist of income (loss) from continuing operations before income taxes, extraordinary items, cumulative effect of accounting changes, equity in net losses of affiliates and fixed charges. “Fixed charges” consist of interest expense and the portion of operating lease expense that represents interest. The following table sets forth the computation of our ratio of earnings to fixed charges for the periods indicated:

	Year Ended December 31,
	2010		2009		2008		2007		2006
Ratio of earnings to fixed charges(1)		N/A		N/A		N/A		N/A		N/A

(1) For the fiscal years ended December 31, 2010, 2009, 2008, 2007, and 2006, our earnings were insufficient to cover fixed charges by $1.5 million, $56.1 million, $77.0 million, $55.9 million and $43.5 million, respectively.

     We have not paid preference dividends during any of the past five fiscal years.

S-9

RISK FACTORS

     An investment in the securities involves a high degree of risk. Before you make a decision to invest in the securities, you should consider carefully the risks described below and discussed under the section captioned “Risk Factors” contained in our Annual Report on Form 10-K for the year ended December 31, 2010, which are incorporated by reference in this prospectus supplement and in the accompanying prospectus in their entirety, together with other information in this prospectus supplement, the accompanying prospectus and the information and documents incorporated by reference. If any of these risks actually occur, our business, operating results, prospects or financial condition could be materially and adversely affected. This could cause the trading price of the securities to decline and you may lose part or all of your investment. Moreover, the risks described are not the only ones that we face. Additional risks not presently known to us or that we currently deem immaterial may also affect our business, operating results, prospects or financial condition.

Risks Relating to this Offering

If you purchase the units sold in this offering, you will experience immediate dilution with respect to the shares of common stock obtained as a result of this offering and future equity issuances.

     The portion of the public offering price per unit in this offering attributable to the common stock is higher than the net tangible book value (deficit) per share of our common stock outstanding prior to this offering. As a result, investors purchasing units in this offering will experience immediate dilution in net tangible book value (deficit) of $0.96 per share of common stock received if we sell all 11,927,034 units that we are offering, or more if we sell fewer units in this offering. In addition, we have issued options and warrants to acquire common stock at prices below the public offering price and have granted restricted stock units that, upon vesting, result in the issuance of common stock for no additional cash consideration. To the extent such outstanding options and warrants are ultimately exercised and restricted stock units vest, there will be further dilution to investors in this offering.

     The issuance of additional shares of our common stock could be dilutive to stockholders if they do not invest in future offerings. Moreover, to the extent that we issue restricted stock units, options or warrants to purchase, or securities convertible into or exchangeable for, shares of our common stock in the future and those restricted stock units, options, warrants or other securities vest or are exercised, converted or exchanged, stockholders may experience further dilution.

We have broad discretion in the use of the net proceeds of this offering and, despite our efforts, we may use the proceeds in a manner that does not improve our operating results or increase the value of your investment.

     We currently anticipate that the net proceeds from the sale of the securities will be used primarily for general corporate purposes, including regulatory activity, clinical trial, research and development, general and administrative and manufacturing expenses. We may also use a portion of the net proceeds to acquire or invest in businesses, products and technologies that complement our business. However, we have not determined the specific allocation of the net proceeds among these potential uses. Our management will have broad discretion over the use and investment of the net proceeds of this offering, and, accordingly, investors in this offering will need to rely upon the judgment of our management with respect to the use of proceeds, with only limited information concerning our specific intentions. These proceeds could be applied in ways that do not improve our operating results or increase the value of your investment. Please see the section entitled “Use of Proceeds” on page S-11 for further information.

S-10

USE OF PROCEEDS

     We estimate the net proceeds to us from the sale of the 11,927,034 units in this offering, after deducting the estimated offering expenses payable by us, to be approximately $15.8 million. If the offered warrants are fully exercised for cash, we will receive additional proceeds of approximately $7.3 million.

     We currently anticipate that the net proceeds from the sale of the securities will be used primarily for general corporate purposes, including regulatory activity, clinical trial, research and development, general and administrative and manufacturing expenses. We may also use a portion of the net proceeds to acquire or invest in businesses, products and technologies that complement our business. As of the date of this prospectus supplement, we do not have any binding commitments or agreements relating to any of these types of transactions. Any such proposed transactions are subject to substantial due diligence, the negotiation of a definitive purchase and sale agreement and ancillary agreements and the receipt of various board of directors, governmental and other approvals. Therefore, there is significant uncertainty whether we will be able to successfully enter into a definitive transaction document and consummate a proposed transaction. Depending upon the size of a transaction, it is possible that a transaction might impact our capital structure by diluting our existing stockholders or increasing our total indebtedness. It is also possible that such a transaction could have a significant impact on our financial results. Pending these uses, we will invest the net proceeds in investment-grade, interest-bearing securities.

S-11

CAPITALIZATION

     The following table sets forth our unaudited cash and capitalization as of December 31, 2010:

• on an actual basis; and

• on an as adjusted basis to give effect to the sale by us of 11,927,034 shares of our common stock in this offering at the public offering price of $1.35 per share, after deducting estimated offering expenses payable by us, but excluding the 4,174,462 shares of common stock issuable upon the exercise of the warrants issued to the investors in this offering.

     This table should be read in conjunction with “Management’s Discussion and Analysis of Financial Condition and Results of Operations” incorporated by reference from our Annual Report on Form 10-K for the year ended December 31, 2010 and our financial statements and notes thereto incorporated by reference in this prospectus supplement and the accompanying prospectus.

	As of December 31, 2010
	Actual			As adjusted (1)
	(in thousands)
Cash, cash equivalents and marketable securities	$	41,449		$	57,300
Long-term obligations		21,809			21,809
Stockholders’ equity:
Preferred stock, $0.0001 par value; 5,000,000 shares authorized; no shares issued or outstanding, actual and as adjusted		—			—
Common stock, $0.0001 par value; 100,000,000 shares authorized; 59,766,328 shares issued and outstanding, actual; 71,693,362 shares issued and outstanding, as adjusted		6			7
Additional paid-in capital		278,386			294,236
Other comprehensive income		2			2
Deficit accumulated during the development stage		(266,104	)		(266,104	)
Total stockholders’ equity		12,290			28,141
Total capitalization	$	34,099		$	49,950

(1) Assumes that all 11,927,034 shares of common stock offered by us pursuant to this prospectus supplement are sold in this offering. Excludes 418,446 shares of our common stock that were issued subsequent to December 31, 2010, but prior to this offering, pursuant to exercises of warrants and stock options, the vesting of restricted stock units and purchases under our employee stock purchase plan. Also excludes the 4,174,462 shares of common stock issuable upon the exercise of the warrants issued to investors in this offering.

S-12

DILUTION

     The net tangible book value of our common stock as of December 31, 2010 was approximately $12.3 million, or $0.21 per share. We calculate net tangible book value per share by dividing our net tangible book value, which is equal to our total tangible assets less total liabilities, by the number of outstanding shares of our common stock. Dilution in net tangible book value per share to new investors represents the difference between the amount per share paid by purchasers of the securities in this offering and the net tangible book value per share of our common stock immediately afterwards.

     Without taking into account any other changes in net tangible book value after December 31, 2010, other than the sale of 11,927,034 units offered by us hereby at a price of $1.35 per unit (and assuming a value per share of common stock offered in each unit of $1.35 per share and attributing no value to the warrants included in each unit) after deducting estimated offering expenses, our adjusted net tangible book value per share of our common stock as of December 31, 2010 would have been $28.1 million or $0.39 per share. The change represents an immediate increase in net tangible book value per share of our common stock of $0.18 per share to existing stockholders and an immediate dilution of $0.96 per share to new investors in this offering. Our net tangible book value calculation assumes no exercise of the warrants offered hereby. The following table illustrates this per share dilution:

Offering price per unit			$	1.35
Net tangible book value per share as of December 31, 2010	$	0.21
Increase per share attributable to new investors		0.18
Pro forma net tangible book value per share after this offering				0.39
Dilution per share to new investors			$	0.96

     Investors that purchase common stock upon exercise of the warrants offered hereby may experience dilution depending on our net tangible book value at the time of exercise. The foregoing does not take into account further dilution to new investors that could occur upon the issuance of additional shares of common stock, the exercise of outstanding warrants, the exercise of outstanding options granted under our equity compensation plans and common stock issuable upon vesting of restricted stock units. To the extent that we sell fewer than 11,927,034 units in this offering, the net tangible book value per share after giving effect to this offering will be less, and the immediate dilution in net tangible book value per share to new investors will be greater.

S-13

PLAN OF DISTRIBUTION

     We are offering the securities directly to select institutional investors, or the purchasers, pursuant to a securities purchase agreement entered into among us and the purchasers. We are not using any placement agent in connection with this offering. Pursuant to the terms and conditions of the securities purchase agreement to be entered into among us and the purchasers, we will sell the purchasers up to 11,927,034 shares of our common stock and warrants to purchase up to 4,174,462 shares of our common stock. We will sell the shares of common stock and the warrants in units, with each unit consisting of one share of common stock and a warrant to purchase 0.35 of a share of common stock, at an initial exercise price of $1.755 per share. Each unit will be sold at a negotiated price of $1.35 per unit.

     We will enter into the securities purchase agreement directly with the purchasers in this offering. However, there is no requirement that any minimum number of units or dollar amount of units be sold in this offering and there can be no assurance that all or any of the units being offered hereby will be sold.

     The securities purchase agreement provides that the obligations of the purchasers are subject to certain conditions precedent, including, among other things, the absence of certain adverse events related to the registration and listing of the shares of our common stock.

     We negotiated the price for the units with the purchasers. The factors considered in determining the price included the recent market price of our common stock, the general condition of the securities market at the time of this offering, the history of, and the prospects, for the industry in which we compete, our past and present operations, and our prospects for future revenues.

     We currently anticipate that closing of this offering will take place on or about May 6, 2011.

     We estimate the total expenses of this offering, which will be payable by us, will be approximately $250,000, which includes legal and printing costs and various other fees associated with registering and listing the securities. After deducting estimated expenses payable by us, we expect the net proceeds from this offering to us to be approximately $15.8 million, assuming that all 11,927,034 units offered by us are sold in this offering.

     On the scheduled closing date, the following will occur:

• we will receive funds in the amount of the aggregate purchase price for the units we sell; and

• we will issue the securities purchased in the offering.

     Under the securities purchase agreement, we have agreed with each of the purchasers that, subject to certain exceptions, we will not, within the 90 days following the closing of this offering, enter into any agreement to issue or announce the issuance or proposed issuance of any shares of our common stock or securities convertible into, exercisable for or exchangeable for shares of our common stock.

S-14

     We have further agreed with each of the purchasers that, subject to certain exceptions, until the earlier of (a) 30 days following the date on which we receive written approval from the FDA for our NDA for AZ-004 or (b) June 30, 2012, we will not issue or enter into any agreement to issue any shares of our common stock or securities convertible into, exercisable for or exchangeable for shares of our common stock under the equity line of credit entered into on May 26, 2010 by and between us and Azimuth Opportunity Ltd or any other similar agreement that permits us to issue equity or debt securities from time to time, or enter into, utilize or draw-down on any mortgages, indentures, borrowings, financings or credit facilities, including “variable rate transactions,” which means transactions in which we issue or sell any debt or equity securities that are convertible into, exchangeable or exercisable for, or include the right to receive additional shares of our common stock either (A) at a conversion price, exercise price or exchange rate or other price that is based upon and/or varies with the trading prices of or quotations for the shares of our common stock at any time after the initial issuance of such debt or equity securities, or (B) with a conversion, exercise or exchange price that is subject to being reset at some future date after the initial issuance of such debt or equity security or upon the occurrence of specified or contingent events directly or indirectly related to our business or the market for our common stock.

     We have also agreed with each of the purchasers that, subject to certain exceptions and limitations, if we issue securities before the earlier of (a) the date on which we receive written approval from the FDA for our NDA for AZ-004 or (b) June 30, 2012, each purchaser shall have the right to purchase its pro rata share (based on subscription amounts) of the proposed securities on the same terms, conditions and price provided for in the proposed issuance of securities.

     The transfer agent for our common stock is Mellon Investor Services, LLC.

     The foregoing descriptions of the securities purchase agreement entered into with investors in this offering are qualified in their entirety by reference to the form of securities purchase agreement and the form of warrant that will be included as exhibits to our Current Report on
Form 8-K that will be filed with the SEC prior to the consummation of this offering.

     Our common stock is listed on the NASDAQ Global Market under the symbol “ALXA”.

S-15

DESCRIPTION OF COMMON STOCK

     The material terms and provisions of our common stock and each other class of our securities that qualifies or limits our common stock are described under “Description of Capital Stock” beginning on page 9 of the accompanying prospectus.

DESCRIPTION OF WARRANTS

     This summary of certain terms and conditions of the warrants is qualified in its entirety by reference to the warrants, the form of which will be included as an exhibit to a Current Report on Form 8-K that will be filed with the SEC prior to the consummation of this offering. Prospective investors should carefully review the terms and conditions set forth in the form of warrant.

     General. The warrants will be issued under the securities purchase agreement among each of the purchasers and us. For a complete description of the terms and conditions applicable to the warrants, you should review a copy of the securities purchase agreement and the form of warrant, each of which will be included as an exhibit to a Current Report on Form 8-K that is filed with the SEC prior to the consummation of this offering. The following is a brief summary of the warrants and is subject in all respects to the provisions contained in the warrants.

     Each warrant entitles the registered holder to purchase the number of shares of our common stock set forth on the cover thereof at an exercise price of $1.755 per share, at any time commencing on the six-month anniversary of its issuance, expected to be November 6, 2011. The warrants are exercisable through the date that is five years after issuance, expected to be May 6, 2016, or the expiration date. The exercise price must be paid (i) in cash, (ii) by net exercise (in which the holder will be entitled to surrender a portion of the shares of common stock subject to the warrant in lieu of cash for the exercise price) or (iii) by a combination of both means at the time of exercise. If the warrants have not been exercised prior to the expiration date, the portion of the warrants that have not been exercised will be automatically exercised by net exercise upon the expiration date. We will not list the warrants on the NASDAQ Global Market, any other national securities exchange or other nationally recognized trading system. The common stock underlying the warrants will be listed on the NASDAQ Global Market. The warrants are transferrable.

     Payment of exercise price. The warrant holders have the option to provide payment of the exercise price of the shares being acquired upon exercise of the warrants (i) in cash, (ii) by net exercise or (iii) by a combination of both means. If there is no effective registration statement registering the common stock issuable upon exercise of the warrants, such warrants may be exercised solely by means of net exercise. The exercise price of the warrants is subject to further adjustment to reflect stock splits and dividends, distributions on our common stock, and similar corporate actions.

     Effect of Corporate Reorganization. If, at any time while warrants are outstanding: (i) we engage in a capital reorganization, (ii) we reclassify our capital stock, (iii) we merge, consolidate or reorganize in one or a series of related transactions in such a manner that our voting securities outstanding prior to the transaction constitute less than 50% of the voting power or economic interests in the resulting entity after the transaction, (iv) we sell or otherwise dispose of all or substantially all of our assets in one or a series of related transactions, (v), we sell shares of our capital stock in one or a series of related transactions that represent at least 50% of the voting power or economic interests in Alexza, or (vi) a single person or group, within the meaning of Section 13(d) or 14(d) of the Exchange Act of 1934, as amended, or the Exchange Act, acquires, directly or indirectly, the beneficial ownership (as defined in Rule 13d-3 under the Exchange Act) of outstanding shares of our capital stock in one or a series of related transactions representing at least 50% of the voting power or economic interests in Alexza, each of (i)-(vi) above we refer to as a corporate reorganization, then the holder of a warrant will have the right thereafter to receive, upon exercise of the warrant, shares of the surviving or acquiring entity, as the case may be, with a Black-Scholes valuation at the time of the corporate reorganization equal to the Black-Scholes valuation of our shares issuable upon exercise of the warrant prior to the corporate reorganization.

     Rights Upon Special Distributions. If, at any time while the warrants are outstanding, we distribute to any holders of our common stock, whether or not accompanied by a purchase, redemption or other acquisition of shares of common stock, (i) evidences of indebtedness, (ii) any of our securities or (iii) any cash, property or other assets,

S-16

then the warrant holders shall be entitled to a pro-rata share of such distribution as though such warrant holders had fully exercised their warrants immediately prior to the record date for such distribution, and we shall pay or distribute such pro-rata share to the warrant holders when paid or distributed to the holders of our common stock.

     Limitation on Exercise. The number of shares of common stock issuable upon exercise of certain of the warrants that may be acquired by the holder of such warrants, upon any exercise of such warrants, shall be limited to the extent necessary to ensure that, following such exercise (or other issuance), the total number of shares of our common stock then beneficially owned by the holder of the warrant and any other persons whose beneficial ownership of shares of our common stock would be aggregated with the warrant holder’s for purposes of Section 13(d) of the Exchange Act, does not exceed 4.999% of the total number of then issued and outstanding shares of our common stock (including for such purpose the shares of our common stock issuable upon such exercise), unless waived by the warrant holder, in which case the ownership limitation threshold would be increased to 9.999%.

S-17

LEGAL MATTERS

     The validity of the securities being offered hereby will be passed upon for us by Cooley LLP, Broomfield, Colorado.

EXPERTS

     Ernst & Young LLP, independent registered public accounting firm, has audited our consolidated financial statements included in our Annual Report on Form 10-K for the year ended December 31, 2010, and the effectiveness of our internal control over financial reporting as of December 31, 2010, as set forth in their reports, which are incorporated by reference in this prospectus supplement and the accompanying prospectus and elsewhere in the registration statement. Our consolidated financial statements are incorporated by reference in reliance on Ernst & Young LLP’s reports, given on their authority as experts in accounting and auditing.

WHERE YOU CAN FIND MORE INFORMATION

     This prospectus supplement is part of a registration statement on Form S-3 that we filed with the SEC. The registration statement that contains this prospectus supplement, including the exhibits to the registration statement, contains additional information about us and the common stock offered by this prospectus supplement.

     We file annual, quarterly and current reports, proxy statements and other information with the SEC. You may read and copy any document we file at the SEC’s Public Reference Room at 100 F Street, N.E., Washington, D.C. 20549. Please call the SEC at 1-800-SEC-0330 for further information on the Public Reference Room. Our public filings, including reports, proxy and information statements, are also available on the SEC’s website at http://www.sec.gov.

INCORPORATION BY REFERENCE

     The SEC allows us to “incorporate by reference” information that we file with it, which means that we can disclose important information to you by referring you to another document that we have filed separately with the SEC. You should read the information incorporated by reference because it is an important part of this prospectus supplement. We incorporate by reference the following information or documents that we have filed with the SEC (Commission File No. 000-51820):

• Our Annual Report on Form 10-K for the fiscal year ended December 31, 2010 filed with the SEC on March 15, 2011;

• Our Annual Report on Form 10-K/A for the fiscal year ended December 31, 2010 filed with the SEC on April 28, 2011;

• Our Current Reports on Form 8-K filed with the SEC on January 18, 2011, January 21, 2011, February 4, 2011, February 22, 2011, and May 3, 2011; and

• The description of our common stock set forth in our registration statement on Form 8-A filed with the SEC on February 23, 2006, including any amendments thereto or reports filed for the purpose of updating this transaction.

     We also incorporate by reference into this prospectus supplement all documents (other than Current Reports furnished under Item 2.02 or Item 7.01 of Form 8-K and exhibits filed on such form that are related to such items) that are filed by us with the SEC pursuant to Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act after the date of this prospectus supplement and until we file a post-effective amendment that indicates the termination of the offering of the securities made by this prospectus supplement. These documents include periodic reports, such as Annual Reports on Form 10-K, Quarterly Reports on Form 10-Q and Current Reports on Form 8-K, as well as proxy statements.

S-18

     Any statement contained herein or in a document incorporated or deemed to be incorporated by reference into this document will be deemed to be modified or superseded for purposes of the document to the extent that a statement contained in this document or any other subsequently filed document that is deemed to be incorporated by reference into this document modifies or supersedes the statement.

     We will furnish without charge to you, upon written or oral request, a copy of any or all of the documents incorporated by reference, including exhibits to those documents. You should direct any requests for documents to Alexza Pharmaceuticals, Inc., Attention: Corporate Secretary, 2091 Stierlin Court, Mountain View, California 94043. Our phone number is (650) 944-7000. In addition, all of the documents incorporated by reference into this prospectus supplement may be accessed via the Internet at our website: http://www.alexza.com. The information contained in, or that can be accessed through, our website is not part of this prospectus supplement or the accompanying prospectus and should not be relied upon in connection with investing in the securities.

S-19

PROSPECTUS

ALEXZA PHARMACEUTICALS, INC.

$75,000,000
COMMON STOCK
PREFERRED STOCK
DEBT SECURITIES
WARRANTS
UNITS

     From time to time, we may sell common stock, preferred stock, debt securities and/or warrants, either individually or in units, with a total value of up to $75,000,000. We may also offer common stock or preferred stock upon conversion of debt securities, common stock upon conversion of preferred stock or common stock, preferred stock or debt securities upon the exercise of warrants. We will specify in any accompanying prospectus supplement the terms of any offering. The prospectus supplement may also update or change the information set forth in this prospectus. The applicable prospectus supplement will contain information, where applicable, as to other listings, if any, on the NASDAQ Global Market or any securities exchange of the securities covered by the prospectus supplement. Our common stock is traded on the NASDAQ Global Market under the trading symbol “ALXA.” On May 25, 2010, the last reported sales price for our common stock was $3.05 per share.

     You should read this prospectus and any prospectus supplement carefully before you invest.

     INVESTING IN OUR SECURITIES INVOLVES A HIGH DEGREE OF RISK. SEE THE SECTION ENTITLED “RISK FACTORS” BEGINNING ON PAGE 8 OF THIS PROSPECTUS.

     THIS PROSPECTUS MAY NOT BE USED TO OFFER OR SELL ANY SECURITIES UNLESS ACCOMPANIED BY A PROSPECTUS SUPPLEMENT.

     We will sell the securities directly to investors, through agents designated from time to time or to or through underwriters or dealers. For additional information on the methods of sale, you should refer to the section entitled “Plan of Distribution.” If any underwriters are involved in the sale of any securities with respect to which this prospectus is being delivered, the names of such underwriters and any applicable commissions or discounts will be set forth in a prospectus supplement. The net proceeds we expect to receive from such sale will also be set forth in a prospectus supplement.

NEITHER THE SECURITIES AND EXCHANGE COMMISSION NOR ANY STATE SECURITIES COMMISSION HAS APPROVED OR DISAPPROVED OF THESE SECURITIES OR PASSED UPON THE ACCURACY OR ADEQUACY OF THIS PROSPECTUS. ANY REPRESENTATION TO THE CONTRARY IS A CRIMINAL OFFENSE.

The date of this Prospectus is May 26, 2010

ABOUT THIS PROSPECTUS

     This prospectus is part of a registration statement on Form S-3 that we filed with the Securities and Exchange Commission, or the SEC, using the “shelf” registration process. Under this shelf registration process, we may sell common stock, preferred stock, debt securities and/or warrants, either individually or in units, in one or more offerings up to a total dollar amount of $75,000,000. This prospectus provides you with a general description of the securities we may offer. Each time we sell common stock, preferred stock, debt securities and/or warrants, either individually or in units, we will provide a prospectus supplement that will contain more specific information about the securities offered. We may also add, update or change in the prospectus supplement any of the information contained in this prospectus. This prospectus, together with applicable prospectus supplements, includes all material information relating to this offering. Please carefully read both this prospectus and any prospectus supplement together with the additional information described below under “Where You Can Find More Information” and “Incorporation By Reference.” THIS PROSPECTUS MAY NOT BE USED TO CONSUMMATE A SALE OF SECURITIES UNLESS IT IS ACCOMPANIED BY A PROSPECTUS SUPPLEMENT.

     You should rely only on the information we have provided or incorporated by reference in this prospectus, any prospectus supplement or any free writing prospectus. We have not authorized anyone to provide you with different information. No dealer, salesperson or other person is authorized to give any information or to represent anything not contained in this prospectus. You must not rely on any unauthorized information or representation. This prospectus is an offer to sell only the securities offered hereby, but only under circumstances and in jurisdictions where it is lawful to do so. You should assume that the information in this prospectus or any prospectus supplement is accurate only as of the date on the front of the document and that any information we have incorporated by reference is accurate only as of the date of the document incorporated by reference, regardless of the time of delivery of this prospectus or any sale of a security.

     This prospectus contains summaries of certain provisions contained in some of the documents described herein, but reference is made to the actual documents for complete information. All of the summaries are qualified in their entirety by the actual documents. Copies of some of the documents referred to herein have been filed, will be filed or will be incorporated by reference as exhibits to the registration statement of which this prospectus is a part, and you may obtain copies of those documents as described below under the section entitled “Where You Can Find Additional Information.”

     This prospectus and the information incorporated herein by reference includes trademarks, service marks and trade names owned by us or others. All trademarks, service marks and trade names included or incorporated by reference into this prospectus or any applicable prospectus supplement are the property of their respective owners.

2

OVERVIEW

     This overview highlights selected information from this prospectus and does not contain all of the information that you need to consider in making your investment decision. You should carefully read the entire prospectus, including the financial data and related notes, risk factors and other information incorporated by reference in this prospectus, and the exhibits to the registration statement of which this prospectus is a part.

     References in this prospectus to “Alexza,” “we,” “us” and “our” refer to Alexza Pharmaceuticals, Inc., a Delaware corporation, and its subsidiaries.

Our Business and Technologies

     We are a pharmaceutical company focused on the research, development and commercialization of novel proprietary products for the acute treatment of central nervous system, or CNS, conditions. All of our product candidates are based on our proprietary technology, the Staccato system. The Staccato system vaporizes an excipient-free drug to form a condensation aerosol that, when inhaled, allows for rapid systemic drug delivery. Because of the particle size of the aerosol, the drug is quickly absorbed through the deep lung into the bloodstream, providing speed of therapeutic onset that is comparable to intravenous, or IV, administration but with greater ease, patient comfort and convenience. In December 2009, we submitted our first New Drug Application, or NDA, to the U.S. Food and Drug Administration, or FDA, for our lead product candidate, AZ-004 (Staccato loxapine). In February 2010, we licensed the U.S. and Canadian commercialization rights to AZ-004 to Biovail Laboratories International SRL, or Biovail. We plan to seek additional commercial partners for AZ-004 outside of the United States and Canada.

     We have five other product candidates in various stages of clinical development, ranging from Phase 1 through late-stage Phase 2. In January 2009, we reduced, and in some cases suspended, the development of these product candidates in order to concentrate our efforts and resources on the clinical, regulatory, manufacturing and commercial development of our lead product candidate. We are conducting a review of our product candidate portfolio and plan to advance the development of at least one product candidate in the second half of 2010. We are seeking partners to support development of our product candidates, but we may develop one or more product candidate without partner support.

     Our clinical-stage product candidates are:

•	AZ-004 (Staccato loxapine). We are developing AZ-004 for the rapid treatment of agitation in patients with schizophrenia or bipolar disorder. In December 2009, we submitted our NDA to the FDA. In February 2010, the FDA accepted our filing and provided us a Prescription Drug User Fee Act, or PDUFA, goal date of October 11, 2010. We believe that the data generated from our clinical and non-clinical studies contained within our NDA submission adequately demonstrate the efficacy and safety of AZ-004 for the rapid treatment of agitation in patients with schizophrenia or bipolar disorder.
	In February 2010, we entered into a collaboration and license agreement, or license agreement, and a manufacture and supply agreement, collectively, the collaboration, with Biovail for AZ-004 (Staccato loxapine) for the treatment of psychiatric and/or neurological indications and the symptoms associated with these indications, including the initial indication of treating agitation in schizophrenia and bipolar disorder patients. The collaboration contemplates that we will be the exclusive supplier of drug product for clinical and commercial uses and have responsibility for the NDA for AZ-004 for the initial indication of rapid treatment of agitation in patients with schizophrenia or bipolar disorder, as well as responsibility for any additional development and regulatory activities required for use in these two patient populations in the outpatient setting. Biovail will be responsible for commercialization for the initial indication and, if it elects, development and commercialization of additional indications for AZ-004 in the United States and Canada.
	Under the terms of the license agreement, Biovail paid us an upfront fee of $40 million, and we may be eligible to receive up to an additional $90 million in milestone payments upon achievement of predetermined regulatory, clinical and commercial manufacturing milestones. We may be subject to certain payment obligations to Biovail, up to $5 million, if we do not meet certain other milestones prior to a termination of the license agreement. We are also eligible to receive tiered royalty payments of 10% to 25% on any net sales of AZ-004. We are responsible for conducting and funding all development and regulatory

3

	activities associated with AZ-004’s initial indication for the rapid treatment of agitation in patients with schizophrenia or bipolar disorder as well as for its possible use in the outpatient setting in these two patient populations. Our obligation to fund the outpatient development efforts is limited to a specified amount, none of which is expected to be incurred in 2010. Biovail is responsible for certain Phase 4 development commitments and related costs and expenses. For additional indications, we have an obligation regarding certain efforts and related costs and expenses, up to a specified amount, and, if it elects, Biovail is responsible for all other development commitments and related costs and expenses.
	Under the terms of the manufacture and supply agreement, we are the exclusive supplier of AZ-004 and have responsibility for the manufacture, packaging, labeling and supply for clinical and commercial uses. Biovail will purchase AZ-004 from us at predetermined transfer prices. The transfer prices depend on the volume of AZ-004 purchases, subject to certain adjustments.
	Either party may terminate the collaboration for the other party’s uncured material breach or bankruptcy. In addition, Biovail has the right to terminate the collaboration (a) upon 90 days written notice for convenience; (b) upon 90 days written notice if the FDA does not approve the AZ-004 NDA for the initial indication for the rapid treatment of agitation in patients with schizophrenia or bipolar disorder; (c) immediately upon written notice for safety reasons or withdrawal of marketing approval; (d) upon 90 days written notice upon certain recalls of the product; or (e) immediately upon written notice within 60 days of termination of the supply agreement under certain circumstances. The supply agreement automatically terminates upon the termination of the license agreement.
•	AZ-007 (Staccato zaleplon). We have completed Phase 1 testing for AZ-007. This product candidate is being developed for the treatment of insomnia in patients who have difficulty falling asleep, including patients who awake in the middle of the night and have difficulty falling back asleep. In the Phase 1 study, AZ-007 delivered an IV-like pharmacokinetic profile with a median time to peak drug concentration of 1.6 minutes. Pharmacodynamics, measured as sedation assessed on a 100 mm visual-analog scale, showed onset of effect as early as 2 minutes after dosing.
•	AZ-001 (Staccato prochlorperazine). During the third quarter of 2008, we conducted an end-of-Phase 2 meeting with the FDA for AZ-001. This product candidate is being developed for the treatment of patients suffering from acute migraine headaches. We believe we have a clear understanding of the development requirements for filing an NDA for this product candidate.
•	AZ-104 (Staccato loxapine, low-dose). AZ-104, a lower-dose version of AZ-004, is being studied for the treatment of patients suffering from acute migraine headaches.
•	AZ-002 (Staccato alprazolam). AZ-002 has completed a Phase 1 clinical trial in healthy subjects and a Phase 2a proof-of-concept clinical trial in panic disorder patients for the treatment of panic attacks, an indication we are not planning to pursue. However, given the safety profile, the successful and reproducible delivery of alprazolam, and the IV-like pharmacological effect demonstrated to date, we are assessing AZ-002 for other possible indications and renewed clinical development.
•	AZ-003 (Staccato fentanyl). We have completed and announced positive results from a Phase 1 clinical trial of AZ-003 in opioid-naïve healthy subjects. This product candidate is being developed for the treatment of patients with acute pain, including patients with breakthrough cancer pain and postoperative patients with acute pain episodes.

     On May 4, 2010, we entered into a Loan and Security Agreement, or loan agreement, with Hercules Technology Growth Capital, Inc., or Hercules. Under the terms of the loan agreement, we have borrowed $15,000,000 at an interest rate of the higher of (i) 10.75% or (ii) 6.5% plus the prime rate as reported in the Wall Street Journal, with a maximum interest rate of 14%, and issued to Hercules a secured term promissory note evidencing the loan. We will make interest only payments for the initial eight months, which will be extended for an additional thee months if we receive FDA approval for the AZ-004 NDA by February 1, 2011. Thereafter, the loan will be repaid in 33 equal monthly installments. The loan agreement limits both the seniority and amount of future debt we may incur. If upon a change of control of Alexza, Hercules reasonably determines that the surviving obligors comprising Alexza are less creditworthy than Alexza was immediately prior to the change of control, then we will be required to prepay all of its obligations under the loan agreement, including all interest that would have accrued had the loan been outstanding through the maturity date. We issued to Hercules a five-year warrant to purchase 376,394 shares of our common stock at a price of $2.69 per share, which was the 50-day average daily weighted average trading price at the time the term sheet for the loan was issued by Hercules.

4

     Other than those licensed to Biovail, we have retained all rights to our product candidates and the Staccato system. We eventually plan to build a U.S.-based specialty sales force to commercialize our product candidates, other than AZ-004, which are approved for marketing and which are intended for specialty pharmaceutical markets. We plan to enter into strategic partnerships with other companies to further develop and commercialize products that are intended for certain markets in the United States and for all of our product candidates in geographic territories outside the United States.

     We were incorporated on December 19, 2000. We have funded our operations primarily through the sale of equity securities, payments received pursuant to collaborations, capital lease and equipment financings and government grants. We have generated $16.9 million in revenues from inception through March 31, 2010, $10 million of which was earned through the license and development agreement or development agreement with Endo Pharmaceuticals, Inc, or Endo, and $6.9 million through United States Small Business Innovation Research grants and drug compound feasibility screening fees. In prior years, we have recognized governmental grant revenue and drug compound/new chemical entity feasibility revenue. However, we expect no grant revenue or drug compound feasibility screening revenue in 2010. In January 2009, we mutually agreed with Endo to terminate the development agreement, at which time we fully fulfilled our obligations under the development agreement, and recognized the remaining $9.5 million of deferred revenues into revenue during the three months ended March 31, 2009. To date, we have received funding totaling $40 million from our Biovail collaboration. We do not expect any material product revenue until at least 2011.

     We have incurred significant losses since our inception. As of March 31, 2010, our deficit accumulated during development stage was $278.0 million and total stockholders’ deficit was $18.8 million. We recognized net losses of $13.4 million, $56.1 million, $77.0 million, $55.9 million and $323.1 million during the three months ended March 31, 2010, the years ended December 31, 2009, 2008 and 2007, and the period from December 19, 2000 (Inception) to March 31, 2010, respectively. We expect our net losses to continue, however we expect a decrease in operating expenses in 2010 as compared to 2009 due to our decreased clinical activity.

General Information

     Our principal executive offices are located at 2091 Stierlin Court, Mountain View, CA 94043 and our telephone number is (650) 944-7000. Our web site address is http://www.alexza.com. The information contained in, or that can be accessed through, our web site is not part of this prospectus.

The Securities We May Offer

     We may offer shares of our common stock and preferred stock, various series of debt securities and/or warrants to purchase any of such securities, either individually or in units, in one or more offerings up to a total dollar amount of $75,000,000 from time to time under this prospectus at prices and on terms to be determined by market conditions at the time of offering. This prospectus provides you with a general description of the securities we may offer. Each time we offer a type or series of securities, we will provide a prospectus supplement that will describe the specific amounts, prices and other important terms of the securities, including, to the extent applicable:

• designation or classification;

• aggregate principal amount or aggregate offering price;

• maturity, if applicable;

• rates and times of payment of interest or dividends, if any;

• redemption, conversion or sinking fund terms, if any;

• voting or other rights, if any;

• conversion prices, if any; and

• important federal income tax considerations.

5

     The prospectus supplement also may add, update or change information contained in this prospectus or in documents we have incorporated by reference. However, no prospectus supplement shall offer a security that is not registered and described in this prospectus at the time of its effectiveness.

THIS PROSPECTUS MAY NOT BE USED TO CONSUMMATE A SALE OF SECURITIES UNLESS IT IS ACCOMPANIED BY A PROSPECTUS SUPPLEMENT.

     We may sell the securities directly to or through agents, underwriters or dealers. We, and our agents or underwriters, reserve the right to accept or reject all or part of any proposed purchase of securities. If we do offer securities through agents or underwriters, we will include in the applicable prospectus supplement:

• the names of those agents or underwriters;

• applicable fees, discounts and commissions to be paid to them; and

• the net proceeds to us.

     Common Stock. We may issue shares of our common stock from time to time. Holders of common stock are entitled to one vote per share on all matters submitted to a vote of stockholders. Subject to any preferences of outstanding shares of preferred stock, holders of common stock are entitled to dividends when and if declared by our board of directors.

     Preferred Stock. We may issue shares of our preferred stock from time to time, in one or more series. Our board of directors will determine the rights, preferences, privileges and restrictions of the preferred stock, including dividend rights, conversion rights, voting rights, terms of redemption, liquidation preferences, sinking fund terms and the number of shares constituting any series or the designation of any series. Convertible preferred stock will be convertible into our common stock or exchangeable for our other securities. Conversion may be mandatory or at your option and would be at prescribed conversion rates.

     Debt Securities. We may offer debt securities from time to time, in one or more series, as either senior or subordinated debt or as senior or subordinated convertible debt. The senior debt securities will rank equally with any other secured and unsubordinated debt. The subordinated debt securities will be subordinate and junior in right of payment, to the extent and in the manner described in the instrument governing the debt, to all of our senior indebtedness. Convertible debt securities will be convertible into or exchangeable for our common stock or our other securities. Conversion may be mandatory or at your option and would be at prescribed conversion rates.

     The debt securities will be issued under one or more documents called indentures, which are contracts between us and a national banking association, as trustee. In this prospectus, we have summarized certain general features of the debt securities. We urge you, however, to read the prospectus supplements related to the series of debt securities being offered, as well as the complete indentures that contain the terms of the debt securities. Forms of indentures may be filed as exhibits to the registration statement of which this prospectus is a part or will be incorporated by reference from reports that we file with the SEC, and supplemental indentures and forms of debt securities containing the terms of debt securities being offered will be filed as exhibits to the registration statement of which this prospectus is a part or will be incorporated by reference from reports that we file with the SEC.

     Warrants. We may issue warrants for the purchase of common stock, preferred stock and/or debt securities in one or more series. We may issue warrants independently or together with common stock, preferred stock and/or debt securities, and the warrants may be attached to or separate from these securities. The warrants will be evidenced by warrant certificates issued under one or more warrant agreements, which are contracts between us and an agent for the holders of the warrants. In this prospectus, we have summarized certain general features of the warrants. We will incorporate by reference into the registration statement of which this prospectus is a part the form of warrant agreement, including a form of warrant certificate, that describes the terms of the series of warrants we are offering before the issuance of the related series of warrants. We urge you to read the prospectus supplements related to the series of warrants being offered, as well as the complete warrant agreements and warrant certificates that contain the terms of the applicable series of warrants.

6

     Units. We may issue units consisting of common stock, preferred stock, debt securities and/or warrants for the purchase of common stock, preferred stock and/or debt securities in one or more series. In this prospectus, we have summarized certain general features of the units. We urge you, however, to read the prospectus supplements related to the series of units being offered, as well as the unit agreements that contain the terms of the units. We will file as exhibits to the registration statement of which this prospectus is a part, or will incorporate by reference from reports that we file with the SEC, the form of unit agreement and any supplemental agreements that describe the terms of the series of units we are offering before the issuance of the related series of units.

     We will enter into the unit agreements with a unit agent. Each unit agent will be a bank or trust company that we select. We will indicate the name and address of the unit agent in the applicable prospectus supplement relating to a particular series of units.

Ratio of Earnings to Fixed Charges

     Our earnings were insufficient to cover fixed charges in each of the years in the five-year period ended December 31, 2009 and for the three-month period ended March 31, 2010. “Earnings” consist of income (loss) from continuing operations before income taxes, extraordinary items, cumulative effect of accounting changes, equity in net losses of affiliates and fixed charges. “Fixed charges” consist of interest expense and the portion of operating lease expense that represents interest. The following table sets forth the computation of our ratio of earnings to fixed charges for the periods indicated:

	Year Ended December 31,					Three Months Ended
	2009	2008	2007	2006	2005	March 31, 2010
Ratio of earnings to fixed charges(1)	N/A	N/A	N/A	N/A	N/A	N/A

(1) For the fiscal years ended December 31, 2009, 2008, 2007, 2006 and 2005, our earnings were insufficient to cover fixed charges by $56.1 million, $77.0 million, $55.9 million, $53.5 million and $32.4 million, respectively. For the three-month period ended March 31, 2010, our earnings were insufficient to cover fixed charges by $13.4 million.

We have not paid preference dividends during any of the past five fiscal years or during the three months ended March 31, 2010.

7

RISK FACTORS

An investment in our securities involves a high degree of risk. Before you make a decision to invest in our securities, you should consider carefully the risks described in the section entitled “Risk Factors” contained in the applicable prospectus supplement and in our most recent Annual Report on Form 10-K and Quarterly Report on Form 10-Q filed with the SEC, as well as any amendment or update thereto reflected in subsequent filings with the SEC. If any of these risks actually occur, our business, operating results, prospects or financial condition could be materially and adversely affected. This could cause the trading price of our securities to decline and you may lose part or all of your investment. Moreover, the risks described are not the only ones that we face. Additional risks not presently known to us or that we currently deem immaterial may also affect our business, operating results, prospects or financial condition.

FORWARD-LOOKING INFORMATION

     This prospectus and the documents that we have filed with the SEC that are incorporated by reference in this prospectus contain forward-looking statements within the meaning of Section 27A of the Securities Act of 1933, as amended, or the Securities Act, and Section 21E of the Securities Exchange Act of 1934, as amended, or the Exchange Act, that are subject to the “safe harbor” created by those sections. Examples of these statements include, but are not limited to, statements regarding the following: the prospects and anticipated timing of us receiving approval to market AZ-004, the implications of interim or final results of our clinical trials, the progress of our research programs, including clinical testing, the extent to which our issued and pending patents may protect our products and technology, the potential of such product candidates to lead to the development of commercial products, our anticipated timing for initiation or completion of our clinical trials for our product candidates, our future operating expenses, our future losses, our future expenditures and the sufficiency of our cash resources.

     These forward-looking statements are generally identified by words such as “may,” “will,” “could,” “would,” “should,” “expect,” “intend,” “plan,” “anticipate,” “believe,” “estimate,” “predict,” “project,” “potential,” “continue,” “ongoing” or the negative of these terms or other comparable terminology, although not all forward-looking statements contain these words. Discussions containing these forward-looking statements may be found, among other places, in “Business” and “Management’s Discussion and Analysis of Financial Condition and Results of Operations” incorporated by reference from our most recent Annual Report on Form 10-K and our Quarterly Reports on Form 10-Q, as well as any amendments thereto reflected in subsequent filings with the SEC. These forward-looking statements involve known and unknown risks, uncertainties and other factors that may cause our actual results, levels of activity, performance or achievements to be materially different from the information expressed or implied by these forward-looking statements. While we believe that we have a reasonable basis for each forward-looking statement contained in this prospectus, we caution you that these statements are based on a combination of facts and factors currently known by us and our projections of the future, about which we cannot be certain. As a result of these factors, we cannot assure you that the forward-looking statements in this prospectus or documents incorporated by reference will prove to be accurate. Furthermore, if our forward-looking statements prove to be inaccurate, the inaccuracy may be material. In light of the significant uncertainties in these forward-looking statements, you should not regard these statements as a representation or warranty by us or any other person that we will achieve our objectives and plans in any specified time frame, or at all. You should not place undue reliance on these forward-looking statements, which apply only as of the date of this prospectus. You should read this prospectus, any accompanying prospectus supplement and the documents incorporated by reference completely and with the understanding that our actual future results may be materially different from what we expect.

     We undertake no obligation to publicly update any forward-looking statements, whether as a result of new information, future events or otherwise. You are advised, however, to consult any further disclosures we make on related subjects in our Annual Reports on Form 10-K, Quarterly Reports on Form 10-Q, Current Reports on Form 8-K and our website.

USE OF PROCEEDS

     Except as described in any prospectus supplement, we currently intend to use the net proceeds from the sale of the securities offered hereby for research and development and general corporate purposes. We may also use a portion of the net proceeds to acquire or invest in businesses, products and technologies that are complementary to our own. Pending these uses, we will invest the net proceeds in investment-grade, interest-bearing securities.

8

DESCRIPTION OF CAPITAL STOCK

     The following description of our capital stock and certain provisions of our restated certificate of incorporation is a summary and is qualified in its entirety by the provisions of our restated certificate of incorporation.

     Our authorized capital stock consists of 100,000,000 shares of common stock, $0.0001 par value, and 5,000,000 shares of preferred stock, $0.0001 par value. As of May 25, 2010, there were 52,908,625 shares of common stock outstanding and no shares of preferred stock outstanding.

Common Stock

     The holders of our common stock are entitled to one vote for each share held of record on all matters submitted to a vote of the stockholders. The holders of common stock are not entitled to cumulative voting rights with respect to the election of directors, and as a consequence, minority stockholders will not be able to elect directors on the basis of their votes alone.

     Subject to preferences that may be applicable to any then-outstanding shares of preferred stock, holders of common stock are entitled to receive ratably such dividends as may be declared by our board of directors out of funds legally available therefor. In the event of a liquidation, dissolution or winding up of us, holders of the common stock are entitled to share ratably in all assets remaining after payment of liabilities and the liquidation preferences of any then outstanding shares of preferred stock. Holders of common stock have no preemptive rights and no right to convert their common stock into any other securities. There are no redemption or sinking fund provisions applicable to our common stock. All outstanding shares of common stock are, and all shares of common stock to be issued under this prospectus will be, fully paid and non-assessable.

Preferred Stock

     Our restated certificate of incorporation provides that our board of directors has the authority, without further action by the stockholders, to issue up to 5,000,000 shares of preferred stock in one or more series and to fix the rights, preferences, privileges and restrictions of this preferred stock, including dividend rights, conversion rights, voting rights, terms of redemption, liquidation preferences, sinking fund terms and the number of shares constituting any series or the designation of a series, without further vote or action by the stockholders.

     We will fix the rights, preferences, privileges and restrictions of the preferred stock of each series in the certificate of designation relating to that series. We will incorporate by reference as an exhibit to the registration statement that includes this prospectus or as an exhibit to a report that we file with the SEC, the form of any certificate of designation that describes the terms of the series of preferred stock we are offering before the issuance of the related series of preferred stock. This description will include:

• the title and stated value;

• the number of shares we are offering;

• the liquidation preference per share;

• the purchase price;

• the dividend rate, period and payment date and method of calculation for dividends;

• whether dividends will be cumulative or non-cumulative and, if cumulative, the date from which dividends will accumulate;

• the procedures for any auction and remarketing, if any;

• the provisions for a sinking fund, if any;

9

• the provisions for redemption or repurchase, if applicable, and any restrictions on our ability to exercise those redemption and repurchase rights;

• any listing of the preferred stock on any securities exchange or market;

• whether the preferred stock will be convertible into our common stock, and, if applicable, the conversion price, or how it will be calculated, and the conversion period;

• whether the preferred stock will be exchangeable into debt securities, and, if applicable, the exchange price, or how it will be calculated, and the exchange period;

• voting rights, if any, of the preferred stock;

• preemptive rights, if any;

• restrictions on transfer, sale or other assignment, if any;

• a discussion of any material or special U.S. federal income tax considerations applicable to the preferred stock;

• the relative ranking and preferences of the preferred stock as to dividend rights and rights if we liquidate, dissolve or wind up our affairs;

• any limitations on issuance of any class or series of preferred stock ranking senior to or on a parity with the series of preferred stock as to dividend rights and rights if we liquidate, dissolve or wind up our affairs; and

• any other specific terms, preferences, rights or limitations of, or restrictions on, the preferred stock.

     If we issue shares of preferred stock under this prospectus, the shares will be fully paid and non-assessable.

     The General Corporation Law of the State of Delaware, the state of our incorporation, provides that the holders of preferred stock will have the right to vote separately as a class on any proposed amendment to our restated certificate of incorporation that would cause certain, specified changes in the rights of the preferred stock. This right is in addition to any voting rights that may be provided for in the applicable certificate of designation.

     The issuance of preferred stock, whether pursuant to this offering or otherwise, could adversely affect the voting power or other rights of holders of our common stock. Preferred stock could be issued quickly with terms designed to delay or prevent a change in control of our company or make removal of management more difficult. Additionally, the issuance of preferred stock may have the effect of decreasing the market price of our common stock.

Anti-Takeover Effects of Provisions of Delaware Law and Our Charter Documents

     Delaware Law. We are subject to Section 203 of the Delaware General Corporation Law, which regulates acquisitions of some Delaware corporations. In general, Section 203 prohibits, with some exceptions, a publicly-held Delaware corporation from engaging in a “business combination” with an “interested stockholder” for a period of three years following the date of the transaction in which the person becomes an interested stockholder, unless:

• our board of directors approved either the business combination or the transaction in which the person became an interested stockholder prior to the time such person became an interested stockholder;

• upon consummation of the transaction that resulted in the person becoming an interested stockholder, the person owned at least 85% of our voting stock outstanding at the time the transaction commenced, excluding shares owned by persons who are directors and also officers of the corporation and shares issued under employee stock plans under which employee participants

10

do not have the right to determine confidentially whether shares held subject to the plan will be tendered in a tender or exchange offer; or

• on or subsequent to the date the person became an interested stockholder, our board of directors approved the business combination and the stockholders other than the interested stockholder authorized the transaction at an annual or special meeting of stockholders by the affirmative vote of at least 66 2/3% of our outstanding stock not owned by the interested stockholder.

     Section 203 defines a “business combination” to include:

• any merger or consolidation involving us and the interested stockholder;

• any sale, transfer, pledge or other disposition of 10% or more of our assets involving the interested stockholder;

• in general, any transaction that results in the issuance or transfer by us of any of our stock to the interested stockholder;

• any transaction involving us that has the effect of increasing the proportionate share of our stock owned by the interested stockholder; and

• the receipt by the interested stockholder of the benefit of any loans, advances, guarantees, pledges, or other financial benefits provided by or through us.

     In general, Section 203 defines an “interested stockholder” as any person who, together with the person’s affiliates and associates, owns, or within three years prior to the time of determination of interested stockholder status did own, 15% or more of a corporation’s outstanding voting stock.

     Section 203 of the Delaware General Corporation Law could depress our stock price and delay, discourage or prohibit transactions not approved in advance by our board of directors, such as takeover attempts that might otherwise involve the payment to our stockholders of a premium over the market price of our common stock.

     Certificate of Incorporation and Bylaw Provisions. Our restated certificate of incorporation includes a number of provisions that may have the effect of deterring hostile takeovers or delaying or preventing changes in control or our management. First, our board of directors can issue up to 5,000,000 shares of preferred stock, with any rights or preferences, including the right to approve or not approve an acquisition or other change in control. Second, our bylaws provide that all stockholder actions must be effected at a duly called meeting of stockholders and not by written consent. Third, our bylaws provide that stockholders seeking to present proposals before a meeting of stockholders or to nominate candidates for election as directors at a meeting of stockholders must provide timely notice in writing. Our bylaws also specify requirements as to the form and content of a stockholder’s notice. These provisions may delay or preclude stockholders from bringing matters before a meeting of stockholders or from making nominations for directors at a meeting of stockholders, which could delay or deter takeover attempts or changes in management. Fourth, our restated certificate of incorporation provides that, subject to the rights of the holders of any outstanding series of our preferred stock, all vacancies, including newly created directorships, may, except as otherwise required by law, be filled by the affirmative vote of a majority of our directors then in office, even if less than a quorum. In addition, our restated certificate of incorporation provides that our board of directors may fix the number of directors by resolution. Fifth, our restated certificate of incorporation does not provide for cumulative voting for our directors. The absence of cumulative voting may make it more difficult for stockholders owning less than a majority of our stock to elect any directors to our board of directors.

Transfer Agent and Registrar

     Mellon Investor Services, LLC has been appointed as the transfer agent and registrar for our common stock.

Listing on the NASDAQ Global Market

     Our common stock is listed on the NASDAQ Global Market under the symbol “ALXA.”

11

DESCRIPTION OF DEBT SECURITIES

     The following description, together with the additional information we include in any applicable prospectus supplements, summarizes the material terms and provisions of the debt securities that we may offer under this prospectus. While the terms we have summarized below will apply generally to any future debt securities we may offer under this prospectus, we will describe the particular terms of any debt securities that we may offer in more detail in the applicable prospectus supplement. The terms of any debt securities we offer under a prospectus supplement may differ from the terms we describe below.

     We will issue the senior debt securities under the senior indenture that we will enter into with the trustee named in the senior indenture. We will issue the subordinated debt securities under the subordinated indenture that we will enter into with the trustee named in the subordinated indenture. We may file the forms of these documents as exhibits to the registration statement that includes this prospectus or incorporate them by reference from a report that we file with the SEC. We use the term “indentures” in this prospectus to refer to both the senior indenture and the subordinated indenture.

     The indentures will be qualified under the Trust Indenture Act of 1939. We use the term “debenture trustee” to refer to either the trustee under the senior indenture or the trustee under the subordinated indenture, as applicable.

     The following summaries of material provisions of the senior debt securities, the subordinated debt securities and the indentures are subject to, and qualified in their entirety by reference to, all the provisions of the indenture applicable to a particular series of debt securities. We urge you to read the applicable prospectus supplements related to the debt securities that we sell under this prospectus, as well as the indenture that contains the terms of the debt securities. Except as we may otherwise indicate, the terms of the senior indenture and the subordinated indenture are identical.

General

     We will describe in each prospectus supplement the following terms relating to a series of debt securities:

• the title;

• the principal amount being offered, and if a series, the total amount authorized and the total amount outstanding;

• any limit on the amount that may be issued;

• whether or not we will issue the series of debt securities in global form, the terms and who the depositary will be;

• the maturity date;

• whether and under what circumstances, if any, we will pay additional amounts on any debt securities held by a person who is not a U.S. person for tax purposes, and whether we can redeem the debt securities if we have to pay such additional amounts;

• the annual interest rate, which may be fixed or variable, or the method for determining the rate and the date interest will begin to accrue, the dates interest will be payable and the regular record dates for interest payment dates or the method for determining such dates;

• whether or not the debt securities will be secured or unsecured, and the terms of any secured debt;

• the terms of the subordination of any series of subordinated debt;

• restrictions on transfer, sale or other assignment, if any;

12

• our right, if any, to defer payment of interest and the maximum length of any such deferral period;

• the date, if any, after which, and the price at which, we may redeem the series of debt securities pursuant to any optional or provisional redemption provisions and the terms of those redemptions provisions;

• the date, if any, on which, and the price at which we are obligated, pursuant to any mandatory sinking fund or analogous fund provisions or otherwise, to redeem, or at the holder’s option to purchase, the series of debt securities and the currency or currency unit in which the debt securities are payable;

• whether the indenture will restrict our ability and/or the ability of our subsidiaries to:

• incur additional indebtedness;

• issue additional securities;

• create liens;

• pay dividends and make distributions in respect of our capital stock and the capital stock of our subsidiaries;

• redeem capital stock;

• place restrictions on our subsidiaries’ ability to pay dividends, make distributions or transfer assets;

• make investments or other restricted payments;

• sell or otherwise dispose of assets;

• enter into sale-leaseback transactions;

• engage in transactions with stockholders and affiliates;

• issue or sell stock of our subsidiaries; or

• effect a consolidation or merger;

• whether the indenture will require us to maintain any interest coverage, fixed charge, cash flow-based, asset-based or other financial ratios;

• a discussion of any material or special U.S. federal income tax considerations applicable to the debt securities;

• information describing any book-entry features;

• provisions for a sinking fund purchase or other analogous fund, if any;

• the denominations in which we will issue the series of debt securities, if other than denominations of $1,000 and any integral multiple thereof; and

• any other specific terms, preferences, rights or limitations of, or restrictions on, the debt securities, including any additional events of default or covenants provided with respect to the debt securities, and any terms that may be required by us or advisable under applicable laws or regulations.

13

Conversion or Exchange Rights

     We will set forth in the prospectus supplement the terms on which a series of debt securities may be convertible into or exchangeable for our common stock or our other securities. We will include provisions as to whether conversion or exchange is mandatory, at the option of the holder or at our option. We may include provisions pursuant to which the number of shares of our common stock or our other securities that the holders of the series of debt securities receive would be subject to adjustment.

Consolidation, Merger or Sale

     Any successor to or acquiror of the indentures must assume all of our obligations under the indentures or the debt securities, as appropriate. If the debt securities are convertible for our other securities or securities of other entities, the person with whom we consolidate or merge or to whom we sell all of our property must make provisions for the conversion of the debt securities into securities that the holders of the debt securities would have received if they had converted the debt securities before the consolidation, merger or sale.

Events of Default Under the Indenture

     The following are events of default under the indentures with respect to any series of debt securities that we may issue:

• if we fail to pay interest when due and payable and our failure continues for 90 days and the time for payment has not been extended or deferred;

• if we fail to pay the principal, premium or sinking fund payment, if any, when due and payable and the time for payment has not been extended or delayed;

• if we fail to observe or perform any other covenant contained in the debt securities or the indentures, other than a covenant specifically relating to another series of debt securities, and our failure continues for 90 days after we receive notice from the debenture trustee or holders of at least 25% in aggregate principal amount of the outstanding debt securities of the applicable series; and

• if specified events of bankruptcy, insolvency or reorganization occur.

     If an event of default with respect to debt securities of any series occurs and is continuing, other than an event of default specified in the last bullet point above, the debenture trustee or the holders of at least 25% in aggregate principal amount of the outstanding debt securities of that series, by notice to us in writing, and to the debenture trustee if notice is given by such holders, may declare the unpaid principal of, premium, if any, and accrued interest, if any, due and payable immediately. If an event of default specified in the last bullet point above occurs with respect to us, the principal amount of and accrued interest, if any, of each issue of debt securities then outstanding shall be due and payable without any notice or other action on the part of the debenture trustee or any holder.

     The holders of a majority in principal amount of the outstanding debt securities of an affected series may waive any default or event of default with respect to the series and its consequences, except defaults or events of default regarding payment of principal, premium, if any, or interest, unless we have cured the default or event of default in accordance with the indenture. Any waiver shall cure the default or event of default.

     Subject to the terms of the indentures, if an event of default under an indenture shall occur and be continuing, the debenture trustee will be under no obligation to exercise any of its rights or powers under such indenture at the request or direction of any of the holders of the applicable series of debt securities, unless such holders have offered the debenture trustee reasonable indemnity. The holders of a majority in principal amount of the outstanding debt securities of any series will have the right to direct the time, method and place of conducting any proceeding for any remedy available to the debenture trustee, or exercising any trust or power conferred on the debenture trustee, with respect to the debt securities of that series, provided that:

• the direction so given by the holder is not in conflict with any law or the applicable indenture or would subject the debenture trustee in its sole discretion to personal liability; and

14

• subject to its duties under the Trust Indenture Act of 1939, the debenture trustee need not take any action that might involve it in personal liability or might be unduly prejudicial to the holders not involved in the proceeding.

     A holder of the debt securities of any series will only have the right to institute a proceeding under the indentures or to appoint a receiver or trustee, or to seek other remedies if:

• the holder has given written notice to the debenture trustee of a continuing event of default with respect to that series;

• the holders of at least 25% in aggregate principal amount of the outstanding debt securities of that series have made written request, and such holders have offered reasonable indemnity to the debenture trustee to institute the proceeding as trustee; and

• the debenture trustee does not institute the proceeding, and does not receive from the holders of a majority in aggregate principal amount of the outstanding debt securities of that series other conflicting directions within 90 days after the notice, request and offer.

     These limitations do not apply to a suit instituted by a holder of debt securities if we default in the payment of the principal, premium, if any, or interest on, the debt securities.

     We will periodically file statements with the debenture trustee regarding our compliance with specified covenants in the indentures.

Modification of Indenture; Waiver

     We and the debenture trustee may change an indenture without the consent of any holders with respect to specific matters:

• to fix any ambiguity, defect or inconsistency in the indenture;

• to comply with the provisions described above under “Consolidation, Merger or Sale;”

• to comply with any requirements of the SEC in connection with the qualification of any indenture under the Trust Indenture Act of 1939;

• to add to, delete from or revise the conditions, limitations and restrictions on the authorized amount, terms or purposes of issue, authentication and delivery of debt securities, as set forth in the indenture;

• to provide for the issuance of and establish the form and terms and conditions of the debt securities of any series as provided under “General,” to establish the form of any certifications required to be furnished pursuant to the terms of the indenture or any series of debt securities, or to add to the rights of the holders of any series of debt securities;

• to evidence and provide for the acceptance of appointment by a successor trustee;

• to provide for uncertificated debt securities in addition to or in place of certificated debt securities;

• to add to our covenants such new covenants, restrictions, conditions or provisions for the protection of the holders, and to make the occurrence, or the occurrence and the continuance, of a default in any such additional covenants, restrictions, conditions or provisions an event of default, or surrender rights of power conferred on us; or

• to change anything that does not materially adversely affect the interests of any holder of debt securities of any series.

     In addition, under the indentures, the rights of holders of a series of debt securities may be changed by us and the debenture trustee with the written consent of the holders of at least a majority in aggregate principal amount of the outstanding debt securities of each

15

series that is affected. However, we and the debenture trustee may only make the following changes with the consent of each holder of any outstanding debt securities affected:

• extending the fixed maturity of the series of debt securities;

• reducing the principal amount, reducing the rate of or extending the time of payment of interest, or reducing any premium payable upon the redemption of any debt securities; or

• reducing the percentage of debt securities, the holders of which are required to consent to any amendment, supplement, modification or waiver.

Discharge

     Each indenture provides that we can elect to be discharged from our obligations with respect to one or more series of debt securities, except for specified obligations, including obligations to:

• register the transfer or exchange of debt securities of the series;

• replace stolen, lost or mutilated debt securities of the series;

• maintain paying agencies;

• hold monies for payment in trust;

• recover excess money held by the debenture trustee;

• compensate and indemnify the debenture trustee; and

• appoint any successor trustee.

     In order to exercise our rights to be discharged, we must deposit with the debenture trustee money or government obligations sufficient to pay all the principal of, any premium, if any, and interest on, the debt securities of the series on the dates payments are due.

Form, Exchange and Transfer

     We will issue the debt securities of each series only in fully registered form without coupons and, unless we otherwise specify in the applicable prospectus supplement, in denominations of $1,000 and any integral multiple thereof. The indentures provide that we may issue debt securities of a series in temporary or permanent global form and as book-entry securities that will be deposited with, or on behalf of, The Depository Trust Company or another depositary named by us and identified in a prospectus supplement with respect to that series. See “Legal Ownership of Securities” for a further description of the terms relating to any book-entry securities.

     At the option of the holder, subject to the terms of the indentures and the limitations applicable to global securities described in the applicable prospectus supplement, the holder of the debt securities of any series can exchange the debt securities for other debt securities of the same series, in any authorized denomination and of like tenor and aggregate principal amount.

     Subject to the terms of the indentures and the limitations applicable to global securities set forth in the applicable prospectus supplement, holders of the debt securities may present the debt securities for exchange or for registration of transfer, duly endorsed or with the form of transfer endorsed thereon duly executed if so required by us or the security registrar, at the office of the security registrar or at the office of any transfer agent designated by us for this purpose. Unless otherwise provided in the debt securities that the holder presents for transfer or exchange, we will make no service charge for any registration of transfer or exchange, but we may require payment of any taxes or other governmental charges.

16

     We will name in the applicable prospectus supplement the security registrar, and any transfer agent in addition to the security registrar, that we initially designate for any debt securities. We may at any time designate additional transfer agents or rescind the designation of any transfer agent or approve a change in the office through which any transfer agent acts, except that we will be required to maintain a transfer agent in each place of payment for the debt securities of each series.

     If we elect to redeem the debt securities of any series, we will not be required to:

• issue, register the transfer of, or exchange any debt securities of that series during a period beginning at the opening of business 15 days before the day of mailing of a notice of redemption of less than all of the outstanding debt securities of the same series that may be selected for redemption and ending at the close of business on the day of the mailing; or

• register the transfer of or exchange any debt securities so selected for redemption, in whole or in part, except the unredeemed portion of any debt securities we are redeeming in part.

Information Concerning the Debenture Trustee

     The debenture trustee, other than during the occurrence and continuance of an event of default under an indenture, undertakes to perform only those duties as are specifically set forth in the applicable indenture. Upon an event of default under an indenture, the debenture trustee must use the same degree of care as a prudent person would exercise or use in the conduct of his or her own affairs. Subject to this provision, the debenture trustee is under no obligation to exercise any of the powers given it by the indentures at the request of any holder of debt securities unless it is offered reasonable security and indemnity against the costs, expenses and liabilities that it might incur.

Payment and Paying Agents

     Unless we otherwise indicate in the applicable prospectus supplement, we will make payment of the interest on any debt securities on any interest payment date to the person in whose name the debt securities, or one or more predecessor securities, are registered at the close of business on the regular record date for the interest.

     We will pay principal of and any premium and interest on the debt securities of a particular series at the office of the paying agents designated by us, except that unless we otherwise indicate in the applicable prospectus supplement, we will make interest payments by check that we will mail to the holder or by wire transfer to certain holders. Unless we otherwise indicate in a prospectus supplement, we will designate the corporate trust office of the debenture trustee as our paying agent for payments with respect to debt securities of each series. We will name in the applicable prospectus supplement any other paying agents that we initially designate for the debt securities of a particular series. We will maintain a paying agent in each place of payment for the debt securities of a particular series.

     All money we pay to a paying agent or the debenture trustee for the payment of the principal of or any premium or interest on any debt securities that remains unclaimed at the end of two years after such principal, premium or interest has become due and payable will be repaid to us, and the holder of the debt security thereafter may look only to us for payment thereof.

Governing Law

     The indentures and the debt securities will be governed by and construed in accordance with the laws of the State of New York, except to the extent that the Trust Indenture Act of 1939 is applicable.

Subordination of Subordinated Debt Securities

     The subordinated debt securities will be unsecured and will be subordinate and junior in priority of payment to certain of our other indebtedness to the extent described in a prospectus supplement. The subordinated indenture does not limit the amount of subordinated debt securities that we may issue. It also does not limit us from issuing any other secured or unsecured debt.

17

DESCRIPTION OF WARRANTS

     The following description, together with the additional information we may include in any applicable prospectus supplements, summarizes the material terms and provisions of the warrants that we may offer under this prospectus and the related warrant agreements and warrant certificates. While the terms summarized below will apply generally to any warrants that we may offer, we will describe the particular terms of any series of warrants in more detail in the applicable prospectus supplement. If we indicate in the prospectus supplement, the terms of any warrants offered under that prospectus supplement may differ from the terms described below. However, no prospectus supplement shall fundamentally change the terms that are set forth in this prospectus or offer a security that is not registered and described in this prospectus at the time of its effectiveness. Specific warrant agreements will contain additional important terms and provisions and will be incorporated by reference as an exhibit to the registration statement that includes this prospectus or as an exhibit to a report that we file with the SEC.

General

     We will describe in the applicable prospectus supplement the terms of the series of warrants, including:

• the offering price and aggregate number of warrants offered;

• the currency for which the warrants may be purchased;

• if applicable, the designation and terms of the securities with which the warrants are issued and the number of warrants issued with each such security or each principal amount of such security;

• if applicable, the date on and after which the warrants and the related securities will be separately transferable;

• in the case of warrants to purchase debt securities, the principal amount of debt securities purchasable upon exercise of one warrant and the price at, and currency in which, this principal amount of debt securities may be purchased upon such exercise;

• in the case of warrants to purchase common stock or preferred stock, the number of shares of common stock or preferred stock, as the case may be, purchasable upon the exercise of one warrant and the price at which these shares may be purchased upon such exercise;

• the effect of any merger, consolidation, sale or other disposition of our business on the warrant agreements and the warrants;

• the terms of any rights to redeem or call the warrants;

• any provisions for changes to or adjustments in the exercise price or number of securities issuable upon exercise of the warrants;

• the dates on which the right to exercise the warrants will commence and expire;

• the manner in which the warrant agreements and warrants may be modified;

• any material or special U.S. federal income tax consequences of holding or exercising the warrants;

• the terms of the securities issuable upon exercise of the warrants; and

• any other specific terms, preferences, rights or limitations of or restrictions on the warrants.

18

     Before exercising their warrants, holders of warrants will not have any of the rights of holders of the securities purchasable upon such exercise, including:

• in the case of warrants to purchase debt securities, the right to receive payments of principal of, or premium, if any, or interest on, the debt securities purchasable upon exercise or to enforce covenants in the applicable indenture; or

• in the case of warrants to purchase common stock or preferred stock, the right to receive dividends, if any, or payments upon our liquidation, dissolution or winding up or to exercise voting rights, if any.

Exercise of Warrants

     Each warrant will entitle the holder to purchase the securities that we specify in the applicable prospectus supplement at the exercise price that we describe in the applicable prospectus supplement. Unless we otherwise specify in the applicable prospectus supplement, holders of the warrants may exercise the warrants at any time up to 5:00 P.M. Eastern Time on the expiration date that we set forth in the applicable prospectus supplement. After the close of business on the expiration date, unexercised warrants will become void.

     Holders of the warrants may exercise the warrants by delivering the warrant certificate representing the warrants to be exercised together with specified information, and paying the required amount to the warrant agent in immediately available funds, as provided in the applicable prospectus supplement. We will set forth on the reverse side of the warrant certificate and in the applicable prospectus supplement the information that the holder of the warrant will be required to deliver to the warrant agent.

     Upon receipt of the required payment and the warrant certificate properly completed and duly executed at the corporate trust office of the warrant agent or any other office indicated in the applicable prospectus supplement, we will issue and deliver the securities purchasable upon such exercise. If fewer than all of the warrants represented by the warrant certificate are exercised, then we will issue a new warrant certificate for the remaining amount of warrants. If we so indicate in the applicable prospectus supplement, holders of the warrants may surrender securities as all or part of the exercise price for warrants.

Enforceability of Rights by Holders of Warrants

     Each warrant agent will act solely as our agent under the applicable warrant agreement and will not assume any obligation or relationship of agency or trust with any holder of any warrant. A single bank or trust company may act as warrant agent for more than one issue of warrants. A warrant agent will have no duty or responsibility in case of any default by us under the applicable warrant agreement or warrant, including any duty or responsibility to initiate any proceedings at law or otherwise, or to make any demand upon us. Any holder of a warrant may, without the consent of the related warrant agent or the holder of any other warrant, enforce by appropriate legal action its right to exercise, and receive the securities purchasable upon exercise of, its warrants.

Outstanding Warrants

     As of May 25, 2010, there were outstanding warrants to purchase 13,103,948 shares of our common stock, of which 5,000,000 of such warrants have an exercise price of $2.26 per share, 376,394 of such warrants have an exercise price of $2.69 per share, 7,296,312 have an exercise price of $2.77 per share, 415,522 have an exercise price of $7.22 per share, 4,116 have an exercise price of $7.29 per share and 11,604 have an exercise price of $7.74 per share. Any of the outstanding warrants may be exercised by applying the value of a portion of the warrant, which is equal to the number of shares issuable under the warrant being exercised multiplied by the fair market value of the security receivable upon the exercise of the warrant, less the per share price, in lieu of payment of the exercise price per share.

     The warrants will expire between March 8, 2013 and October 5, 2016, unless earlier exercised.

19

DESCRIPTION OF UNITS

     The following description, together with the additional information we may include in any applicable prospectus supplements, summarizes the material terms and provisions of the units that we may offer under this prospectus. While the terms we have summarized below will apply generally to any units that we may offer under this prospectus, we will describe the particular terms of any series of units in more detail in the applicable prospectus supplement. The terms of any units offered under a prospectus supplement may differ from the terms described below.

     We will file as exhibits to the registration statement of which this prospectus is a part, or will incorporate by reference from reports that we file with the SEC, the form of unit agreement that describes the terms of the series of units we are offering, and any supplemental agreements, before the issuance of the related series of units. The following summaries of material terms and provisions of the units are subject to, and qualified in their entirety by reference to, all the provisions of the unit agreement and any supplemental agreements applicable to a particular series of units. We urge you to read the applicable prospectus supplements related to the particular series of units that we sell under this prospectus, as well as the complete unit agreement and any supplemental agreements that contain the terms of the units.

General

     We may issue units comprised of one or more debt securities, shares of common stock, shares of preferred stock and warrants in any combination. Each unit will be issued so that the holder of the unit is also the holder of each security included in the unit. Thus, the holder of a unit will have the rights and obligations of a holder of each included security. The unit agreement under which a unit is issued may provide that the securities included in the unit may not be held or transferred separately, at any time or at any time before a specified date.

     We will describe in the applicable prospectus supplement the terms of the series of units, including:

• the designation and terms of the units and of the securities comprising the units, including whether and under what circumstances those securities may be held or transferred separately;

• any provisions of the governing unit agreement that differ from those described below; and

• any provisions for the issuance, payment, settlement, transfer or exchange of the units or of the securities comprising the units.

     The provisions described in this section, as well as those described under “Description of Capital Stock,” “Description of Debt Securities” and “Description of Warrants” will apply to each unit and to any common stock, preferred stock, debt security or warrant included in each unit, respectively.

Issuance in Series

     We may issue units in such amounts and in such numerous distinct series as we determine.

Enforceability of Rights by Holders of Units

     Each unit agent will act solely as our agent under the applicable unit agreement and will not assume any obligation or relationship of agency or trust with any holder of any unit. A single bank or trust company may act as unit agent for more than one series of units. A unit agent will have no duty or responsibility in case of any default by us under the applicable unit agreement or unit, including any duty or responsibility to initiate any proceedings at law or otherwise, or to make any demand upon us. Any holder of a unit may, without the consent of the related unit agent or the holder of any other unit, enforce by appropriate legal action its rights as holder under any security included in the unit.

20

LEGAL OWNERSHIP OF SECURITIES

     We can issue securities in registered form or in the form of one or more global securities. We describe global securities in greater detail below. We refer to those persons who have securities registered in their own names on the books that we or any applicable trustee, depositary or warrant agent maintain for this purpose as the “holders” of those securities. These persons are the legal holders of the securities. We refer to those persons who, indirectly through others, own beneficial interests in securities that are not registered in their own names as “indirect holders” of those securities. As we discuss below, indirect holders are not legal holders and investors in securities issued in book-entry form or in street name will be indirect holders.

Book-Entry Holders

     We may issue securities in book-entry form only, as we will specify in the applicable prospectus supplement. This means securities may be represented by one or more global securities registered in the name of a financial institution that holds them as depositary on behalf of other financial institutions that participate in the depositary’s book-entry system. These participating institutions, which are referred to as participants, in turn, hold beneficial interests in the securities on behalf of themselves or their customers.

     Only the person in whose name a security is registered is recognized as the holder of that security. Securities issued in global form will be registered in the name of the depositary or its participants. Consequently, for securities issued in global form, we will recognize only the depositary as the holder of the securities, and we will make all payments on the securities to the depositary. The depositary passes along the payments it receives to its participants, which in turn pass the payments along to their customers who are the beneficial owners. The depositary and its participants do so under agreements they have made with one another or with their customers; they are not obligated to do so under the terms of the securities.

     As a result, investors in a book-entry security will not own securities directly. Instead, they will own beneficial interests in a global security, through a bank, broker or other financial institution that participates in the depositary’s book-entry system or holds an interest through a participant. As long as the securities are issued in global form, investors will be indirect holders, and not holders, of the securities.

Street Name Holders

     We may terminate a global security or issue securities in non-global form. In these cases, investors may choose to hold their securities in their own names or in “street name.” Securities held by an investor in street name would be registered in the name of a bank, broker or other financial institution that the investor chooses, and the investor would hold only a beneficial interest in those securities through an account he or she maintains at that institution.

     For securities held in street name, we will recognize only the intermediary banks, brokers and other financial institutions in whose names the securities are registered as the holders of those securities, and we will make all payments on those securities to them. These institutions pass along the payments they receive to their customers who are the beneficial owners, but only because they agree to do so in their customer agreements or because they are legally required to do so. Investors who hold securities in street name will be indirect holders, not holders, of those securities.

Legal Holders

     Our obligations, as well as the obligations of any applicable trustee and of any third parties employed by us or a trustee, run only to the legal holders of the securities. We do not have obligations to investors who hold beneficial interests in global securities, in street name or by any other indirect means. This will be the case whether an investor chooses to be an indirect holder of a security or has no choice because we are issuing the securities only in global form.

     For example, once we make a payment or give a notice to the holder, we have no further responsibility for the payment or notice even if that holder is required, under agreements with depositary participants or customers or by law, to pass it along to the indirect holders but does not do so. Similarly, we may want to obtain the approval of the holders to amend an indenture, to relieve us of the consequences of a default or of our obligation to comply with a particular provision of the indenture or for other purposes. In such an

21

event, we would seek approval only from the holders, and not the indirect holders, of the securities. Whether and how the holders contact the indirect holders is up to the holders.

Special Considerations For Indirect Holders

     If you hold securities through a bank, broker or other financial institution, either in book-entry form or in street name, you should check with your own institution to find out:

• how it handles securities payments and notices;

• whether it imposes fees or charges;

• how it would handle a request for the holders’ consent, if ever required;

• whether and how you can instruct it to send you securities registered in your own name so you can be a holder, if that is permitted in the future;

• how it would exercise rights under the securities if there were a default or other event triggering the need for holders to act to protect their interests; and

• if the securities are in book-entry form, how the depositary’s rules and procedures will affect these matters.

Global Securities

     A global security is a security that represents one or any other number of individual securities held by a depositary. Generally, all securities represented by the same global securities will have the same terms.

     Each security issued in book-entry form will be represented by a global security that we deposit with and register in the name of a financial institution or its nominee that we select. The financial institution that we select for this purpose is called the depositary. Unless we specify otherwise in the applicable prospectus supplement, The Depository Trust Company, New York, New York, known as DTC, will be the depositary for all securities issued in book-entry form.

     A global security may not be transferred to or registered in the name of anyone other than the depositary, its nominee or a successor depositary, unless special termination situations arise. We describe those situations below under “Special Situations When a Global Security Will Be Terminated.” As a result of these arrangements, the depositary, or its nominee, will be the sole registered owner and holder of all securities represented by a global security, and investors will be permitted to own only beneficial interests in a global security. Beneficial interests must be held by means of an account with a broker, bank or other financial institution that in turn has an account with the depositary or with another institution that does. Thus, an investor whose security is represented by a global security will not be a holder of the security, but only an indirect holder of a beneficial interest in the global security.

     If the prospectus supplement for a particular security indicates that the security will be issued in global form only, then the security will be represented by a global security at all times unless and until the global security is terminated. If termination occurs, we may issue the securities through another book-entry clearing system or decide that the securities may no longer be held through any book-entry clearing system.

Special Considerations For Global Securities

     As an indirect holder, an investor’s rights relating to a global security will be governed by the account rules of the investor’s financial institution and of the depositary, as well as general laws relating to securities transfers. We do not recognize an indirect holder as a holder of securities and instead deal only with the depositary that holds the global security.

22

     If securities are issued only in the form of a global security, an investor should be aware of the following:

• An investor cannot cause the securities to be registered in his or her name, and cannot obtain non-global certificates for his or her interest in the securities, except in the special situations we describe below;

• An investor will be an indirect holder and must look to his or her own bank or broker for payments on the securities and protection of his or her legal rights relating to the securities, as we describe above;

• An investor may not be able to sell interests in the securities to some insurance companies and to other institutions that are required by law to own their securities in non-book-entry form;

• An investor may not be able to pledge his or her interest in a global security in circumstances where certificates representing the securities must be delivered to the lender or other beneficiary of the pledge in order for the pledge to be effective;

• The depositary’s policies, which may change from time to time, will govern payments, transfers, exchanges and other matters relating to an investor’s interest in a global security. We and any applicable trustee have no responsibility for any aspect of the depositary’s actions or for its records of ownership interests in a global security. We and the trustee also do not supervise the depositary in any way;

• The depositary may, and we understand that DTC will, require that those who purchase and sell interests in a global security within its book-entry system use immediately available funds, and your broker or bank may require you to do so as well; and

• Financial institutions that participate in the depositary’s book-entry system, and through which an investor holds its interest in a global security, may also have their own policies affecting payments, notices and other matters relating to the securities.

     There may be more than one financial intermediary in the chain of ownership for an investor. We do not monitor and are not responsible for the actions of any of those intermediaries.

Special Situations When A Global Security Will Be Terminated

     In a few special situations described below, the global security will terminate and interests in it will be exchanged for physical certificates representing those interests. After that exchange, the choice of whether to hold securities directly or in street name will be up to the investor. Investors must consult their own banks or brokers to find out how to have their interests in securities transferred to their own name, so that they will be direct holders. We have described the rights of holders and street name investors above.

     The global security will terminate when the following special situations occur:

• if the depositary notifies us that it is unwilling, unable or no longer qualified to continue as depositary for that global security and we do not appoint another institution to act as depositary within 90 days;

• if we notify any applicable trustee that we wish to terminate that global security; or

• if an event of default has occurred with regard to securities represented by that global security and has not been cured or waived.

     The prospectus supplement may also list additional situations for terminating a global security that would apply only to the particular series of securities covered by the prospectus supplement. When a global security terminates, the depositary, and not we or any applicable trustee, is responsible for deciding the names of the institutions that will be the initial direct holders.

23

PLAN OF DISTRIBUTION

     We may sell the securities from time to time pursuant to underwritten public offerings, negotiated transactions, block trades or a combination of these methods. We may sell securities through underwriters or dealers, through agents or directly to one or more purchasers. We may distribute securities from time to time in one or more transactions:

• at a fixed price or prices, which may be changed;

• at market prices prevailing at the time of sale;

• at prices related to such prevailing market prices; or

• at negotiated prices.

A prospectus supplement or supplements will describe the terms of the offering of the securities, including:

• the name or names of any underwriters, if any;

• the purchase price of the securities and the proceeds we will receive from the sale;

• any over-allotment options under which underwriters may purchase additional securities from us;

• any agency fees or underwriting discounts and other items constituting agents’ or underwriters’ compensation;

• any public offering price;

• any discounts or concessions allowed or reallowed or paid to dealers; and

• any securities exchange or market on which the securities may be listed.

     Only underwriters named in the prospectus supplement are underwriters of the securities offered by the prospectus supplement.

     If underwriters are used in the sale, they will acquire the securities for their own account and may resell the securities from time to time in one or more transactions at a fixed public offering price or at varying prices determined at the time of sale. The obligations of the underwriters to purchase the securities will be subject to the conditions set forth in the applicable underwriting agreement. We may offer the securities to the public through underwriting syndicates represented by managing underwriters or by underwriters without a syndicate. Subject to certain conditions, the underwriters will be obligated to purchase all of the securities offered by the prospectus supplement, other than securities covered by any over-allotment option. Any public offering price and any discounts or concessions allowed or reallowed or paid to dealers may change from time to time. We may use underwriters with whom we have a material relationship. We will describe in the prospectus supplement, naming the underwriter, the nature of any such relationship.

     We may sell securities directly or through agents we designate from time to time. We will name any agent involved in the offering and sale of securities and we will describe any commissions we will pay the agent in the prospectus supplement. Unless the prospectus supplement states otherwise, our agent will act on a best-efforts basis for the period of its appointment.

     We may authorize agents or underwriters to solicit offers by certain types of institutional investors to purchase securities from us at the public offering price set forth in the prospectus supplement pursuant to delayed delivery contracts providing for payment and delivery on a specified date in the future. We will describe the conditions to these contracts and the commissions we must pay for solicitation of these contracts in the prospectus supplement.

     We may provide agents and underwriters with indemnification against civil liabilities related to this offering, including liabilities under the Securities Act, or contribution with respect to payments that the agents or underwriters may make with respect to these liabilities. Agents and underwriters may engage in transactions with, or perform services for, us in the ordinary course of business.

24

     All securities we offer, other than common stock, will be new issues of securities with no established trading market. Any underwriters may make a market in these securities, but will not be obligated to do so and may discontinue any market making at any time without notice. We cannot guarantee the liquidity of the trading markets for any securities.

     Any underwriter may engage in overallotment, stabilizing transactions, short covering transactions and penalty bids in accordance with Regulation M under the Exchange Act. Overallotment involves sales in excess of the offering size, which create a short position. Stabilizing transactions permit bids to purchase the underlying security so long as the stabilizing bids do not exceed a specified maximum. Short covering transactions involve purchases of the securities in the open market after the distribution is completed to cover short positions. Penalty bids permit the underwriters to reclaim a selling concession from a dealer when the securities originally sold by the dealer are purchased in a covering transaction to cover short positions. Those activities may cause the price of the securities to be higher than it would otherwise be. If commenced, the underwriters may discontinue any of the activities at any time.

     Any underwriters that are qualified market makers on the NASDAQ Global Market may engage in passive market making transactions in the securities on the NASDAQ Global Market in accordance with Rule 103 of Regulation M during the business day prior to the pricing of the offering, before the commencement of offers or sales of the securities. Passive market makers must comply with applicable volume and price limitations and must be identified as passive market makers. In general, a passive market maker must display its bid at a price not in excess of the highest independent bid for such security; if all independent bids are lowered below the passive market maker’s bid, however, the passive market maker’s bid must then be lowered when certain purchase limits are exceeded.

     In compliance with guidelines of the Financial Industry Regulatory Authority, or FINRA, the maximum compensation to be received by any FINRA member or independent broker dealer may not exceed 8% of the aggregate amount of the securities offered pursuant to this prospectus and any applicable prospectus supplement.

Equity Line of Credit

     On May 26, 2010, we entered into what is sometimes termed an equity line of credit arrangement with Azimuth Opportunity Ltd., or Azimuth. Specifically, we entered into a Common Stock Purchase Agreement with Azimuth, or the Purchase Agreement, that provides that, upon the terms and subject to the conditions set forth therein, Azimuth is committed to purchase up to the lesser of $25,000,000 of our common stock, or 10,581,724 shares of our common stock, which is equal to one share less than twenty percent of our issued and outstanding shares of common stock on the effective date of the Purchase Agreement, over the 24-month term of the Purchase Agreement. From time to time over the term of the Purchase Agreement, and at our sole discretion, we may present Azimuth with draw down notices to purchase our common stock over ten consecutive trading days or such other period mutually agreed upon by us and Azimuth, or the draw down period, with each draw down subject to limitations based on the price of our common stock and a limit of 2.5% of our market capitalization at the time of such draw down. We are able to present Azimuth with up to 24 draw down notices during the term of the Purchase Agreement, with only one such draw down notice allowed per draw down period and a minimum of five trading days required between each draw down period.

     Once presented with a draw down notice, Azimuth is required to purchase a pro rata portion of the shares on each trading day during the trading period on which the daily volume weighted average price for our common stock equals or exceeds a threshold price determined by us for such draw down. The per share purchase price for these shares equals the daily volume weighted average price of our common stock on each date during the draw down period on which shares are purchased, less a discount ranging from 5.00% to 6.75%, based on the threshold price specified in our draw down notice. If the daily volume weighted average price of our common stock falls below the threshold price on any trading day during a draw down period, the Purchase Agreement provides that Azimuth will not be required to purchase the pro-rata portion of shares of common stock allocated to that day. However, at its election, Azimuth may buy the pro-rata portion of shares allocated to that day at the threshold price less the applicable discount described above.

     The Purchase Agreement also provides that from time to time and at our sole discretion we may grant Azimuth the right to exercise options to purchase additional shares of our common stock during each draw down period for an amount of shares specified by us based on the trading price of our common stock. Upon Azimuth’s exercise of an option, we would sell to Azimuth the shares of our common stock subject to the option at a price equal to the greater of the daily volume weighted average price of our common

25

stock on the day Azimuth notifies us of its election to exercise its option or the threshold price for the option determined by us, less a discount calculated in the same manner as it is calculated in the draw down notices.

     In addition to our issuance of shares of common stock to Azimuth pursuant to the Purchase Agreement, our Registration Statement on Form S-3 (File No. 333-166514), or the Registration Statement, also covers the sale of those shares from time to time by Azimuth to the public. Azimuth is an “underwriter” within the meaning of Section 2(a)(11) of the Securities Act.

     Azimuth has informed us that it will use an unaffiliated broker-dealer to effectuate all sales, if any, of common stock that it may purchase from us pursuant to the Purchase Agreement. Such sales will be made on the NASDAQ Global Market at prices and at terms then prevailing or at prices related to the then current market price. Each such unaffiliated broker-dealer will be an underwriter within the meaning of Section 2(a)(11) of the Securities Act. Azimuth has informed us that each such broker-dealer will receive commissions from Azimuth that will not exceed customary brokerage commissions. Azimuth also will pay other expenses associated with the sale of the common stock it acquires pursuant to the Purchase Agreement.

     The shares of common stock may be sold in one or more of the following manners:

• ordinary brokerage transactions and transactions in which the broker solicits purchasers; or

• a block trade in which the broker or dealer so engaged will attempt to sell the shares as agent, but may position and resell a portion of the block as principal to facilitate the transaction.

     Azimuth has agreed that during the term of and for a period of 90 days after the termination of the Purchase Agreement, neither Azimuth nor any of its affiliates will, directly or indirectly, sell any of our securities except the shares that it owns or has the right to purchase pursuant to the provisions of a draw down notice. Azimuth has agreed that prior to and during the periods listed above neither it nor any of its affiliates will enter into a short position with respect to shares of our common stock except that Azimuth may sell shares that it is obligated to purchase under a pending draw down notice but has not yet taken possession of so long as Azimuth covers any such sales with the shares purchased pursuant to such draw down notice. Azimuth has further agreed that during the periods listed above it will not grant any option to purchase or acquire any right to dispose or otherwise dispose for value of any shares of our common stock or any securities convertible into, or exchangeable for, or warrants to purchase, any shares of our common stock, or enter into any swap, hedge or other agreement that transfers, in whole or in part, the economic risk of ownership of our common stock, except for the sales permitted by the prior two sentences.

     In addition, Azimuth and any unaffiliated broker-dealer will be subject to liability under the federal securities laws and must comply with the requirements of the Securities Act and the Exchange Act, including, without limitation, Rule 10b-5 and Regulation M under the Exchange Act. These rules and regulations may limit the timing of purchases and sales of shares of common stock by Azimuth or any unaffiliated broker-dealer. Under these rules and regulations, Azimuth and any unaffiliated broker-dealer:

• may not engage in any stabilization activity in connection with our securities;

• must furnish each broker that offers shares of our common stock covered by the prospectus that is a part of our Registration Statement with the number of copies of such prospectus and any prospectus supplement that are required by each broker; and

• may not bid for or purchase any of our securities or attempt to induce any person to purchase any of our securities other than as permitted under the Exchange Act.

     These restrictions may affect the marketability of the shares of common stock purchased and sold by Azimuth and any unaffiliated broker-dealer.

     We have agreed to indemnify and hold harmless Azimuth and each person who controls Azimuth against certain liabilities, including certain liabilities under the Securities Act. We have agreed to pay up to $35,000 of Azimuth’s reasonable attorneys’ fees and expenses (exclusive of disbursements and out-of-pocket expenses) incurred by Azimuth in connection with the preparation, negotiation, execution and delivery of the Purchase Agreement and related transaction documentation. We have also agreed to pay all reasonable attorneys’ fees and expenses incurred by Azimuth in connection with due diligence during each calendar quarter in which

26

no shares of common stock have been purchased or sold pursuant to the Purchase Agreement because we did not deliver a draw down notice, up to $5,000 in each such calendar quarter. Further, we have agreed that if we issue a draw down notice and fail to deliver the shares to Azimuth on the applicable settlement date, and such failure continues for ten trading days, we will pay Azimuth liquidated damages in cash or restricted shares of our common stock, at the option of Azimuth.

     Azimuth has agreed to indemnify and hold harmless us and each of our directors, officers and persons who control us against certain liabilities, including certain liabilities under the Securities Act that may be based upon written information furnished by Azimuth to us for inclusion in a prospectus or prospectus supplement related to this transaction.

     Upon each sale of our common stock to Azimuth under the Purchase Agreement, we have also agreed to pay Reedland Capital Partners, an Institutional Division of Financial West Group, member FINRA/SIPC, a placement fee equal to 0.75% of the aggregate dollar amount of common stock purchased by Azimuth. We have agreed to indemnify and hold harmless Reedland against certain liabilities, including certain liabilities under the Securities Act.

LEGAL MATTERS

     The validity of the securities being offered hereby will be passed upon for us by Cooley LLP, Broomfield, Colorado.

EXPERTS

     Ernst & Young LLP, independent registered public accounting firm, has audited our consolidated financial statements included in our Annual Report on Form 10-K for the year ended December 31, 2009, and the effectiveness of our internal control over financial reporting as of December 31, 2009, as set forth in their reports, which are incorporated by reference in this prospectus and elsewhere in the registration statement. Our consolidated financial statements are incorporated by reference in reliance on Ernst & Young LLP’s reports, given on their authority as experts in accounting and auditing.

WHERE YOU CAN FIND MORE INFORMATION

     We are a reporting company and file annual, quarterly and current reports, proxy statements and other information with the SEC. We have filed with the SEC a registration statement on Form S-3 under the Securities Act with respect to the securities we are offering under this prospectus. This prospectus does not contain all of the information set forth in the registration statement and the exhibits to the registration statement. For further information with respect to us and the securities we are offering under this prospectus, we refer you to the registration statement and the exhibits and schedules filed as a part of the registration statement. You may read and copy the registration statement, as well as our reports, proxy statements and other information we file with the SEC, at the SEC’s public reference room at 100 F Street, N.E., Washington, D.C. 20549. Please call the SEC at 1-800-SEC-0330 for more information about the operation of the public reference room. Our SEC filings are also available at the SEC’s web site at http://www.sec.gov.

INCORPORATION BY REFERENCE

     The SEC allows us to “incorporate by reference” information that we file with it, which means that we can disclose important information to you by referring you to another document that we have filed separately with the SEC. You should read the information incorporated by reference because it is an important part of this prospectus. We incorporate by reference the following information or documents that we have filed with the SEC (Commission File No. 000-51820):

• Our Current Reports on Form 8-K filed with the SEC on February 11, 2010, February 16, 2010, March 11, 2010, May 5, 2010, May 24, 2010 and May 26, 2010;

• Our Annual Report on Form 10-K for the fiscal year ended December 31, 2009 filed with the SEC on March 9, 2010 (the “2009 Form 10-K”);

• The information specifically incorporated by reference into the 2009 Form 10-K from our definitive proxy statement on Schedule 14A filed with the SEC on April 6, 2010;

27

• Our Quarterly Report on Form 10-Q for the three-month period ended March 31, 2010 filed with the SEC on May 10, 2010; and

• The description of our common stock set forth in our registration statement on Form 8-A filed with the SEC on February 23, 2006, including any amendments thereto or reports filed for the purpose of updating this transaction.

     We also incorporate by reference into this prospectus all documents (other than Current Reports furnished under Item 2.02 or Item 7.01 of Form 8-K and exhibits filed on such form that are related to such items) that are filed by us with the SEC pursuant to Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act after the date of this prospectus and until we file a post-effective amendment that indicates the termination of the offering of the securities made by this prospectus. These documents include periodic reports, such as Annual Reports on Form 10-K, Quarterly Reports on Form 10-Q and Current Reports on Form 8-K, as well as proxy statements.

     Any statement contained herein or in a document incorporated or deemed to be incorporated by reference into this document will be deemed to be modified or superseded for purposes of the document to the extent that a statement contained in this document or any other subsequently filed document that is deemed to be incorporated by reference into this document modifies or supersedes the statement.

     We will furnish without charge to you, upon written or oral request, a copy of any or all of the documents incorporated by reference, including exhibits to those documents. You should direct any requests for documents to Alexza Pharmaceuticals, Inc., Attention: Corporate Secretary, 2091 Stierlin Court, Mountain View, California 94043. Our phone number is (650) 944-7000. In addition, all of the documents incorporated by reference into this prospectus may be accessed via the Internet at our website: http://www.alexza.com.

28