Exhibit 3.3

BY-LAWS

OF

INSYS THERAPEUTICS, INC.

(a Delaware corporation)

ARTICLE I

OFFICES

SECTION 1. The registered office shall be in the City of Dover, County of Kent, State of Delaware.

SECTION 2. The Corporation may also have offices at such other places both within and without the State of Delaware as the board of directors may from time to time determine or the business of the Corporation may require.

ARTICLE II

MEETINGS OF STOCKHOLDERS

SECTION 1. All meetings of the stockholders shall be held at any place within or outside the State of Delaware as shall be designated from time to time by the board of directors. In the absence of any such designation, stockholders’ meetings shall be held at the principal executive office of the Corporation.

SECTION 2. An annual meeting of stockholders shall be held on the first Monday of December. At each meeting directors shall be elected and any other proper business may be transacted.

SECTION 3. A majority of the stock issued and outstanding and entitled to vote at any meeting of stockholders, the holders of which are present in person or represented by proxy, shall constitute a quorum for the transaction of business except as otherwise provided by law, by the Certificate of Incorporation, or by these By-Laws. A quorum, once established, shall not be broken by the withdrawal of enough votes to leave less than a quorum and the votes present may continue to transact business until adjournment. If, however, such quorum shall not be present or represented at any meeting of the stockholders, a majority of the voting stock represented in person or by proxy may adjourn the meeting from time to time, without notice other than announcement at the meeting, until a quorum shall be present or represented. At such adjourned meeting at which a quorum shall be present or represented, any business may be transacted which might have been transacted at the meeting as originally notified. If the adjournment is for more than 30 days, or if after the adjournment a new record date is fixed for the adjourned meeting, a notice of the adjourned meeting shall be given to each stockholder of record entitled to vote thereat.

SECTION 4. When a quorum is present at any meeting, the vote of the holders of a majority of the stock having voting power present in person or represented by proxy shall decide any question brought before such meeting, unless the question is one upon which by express provision of law, or the Certificate of Incorporation, or these By-Laws, a different vote is required in which case such express provision shall govern and control the decision of such question.

SECTION 5. At each meeting of the stockholders, each stockholder having the right to vote may vote in person or may authorize another person or persons to act for him/her by proxy appointed by an instrument in writing subscribed by such stockholder and bearing a date not more than three years prior to said meeting, unless said instrument provides for a longer period. All proxies must be filed with the secretary of the Corporation at the beginning of each meeting in order to be counted in any vote at the meeting. Each stockholder shall have one vote for each share of stock having voting power, registered in his/her name on the books of the Corporation on the record date set by the board of directors as provided in Article V, Section 6 hereof. All elections shall be had and all questions decided by a plurality vote.

SECTION 6. Special meetings of the stockholders, for any purpose, or purposes, unless otherwise prescribed by statute or by the Certificate of Incorporation, may be called by the president and shall be called by the president or the secretary at the request in writing of a majority of the board of directors, or at the request in writing of stockholders owning a majority in amount of the entire capital stock of the Corporation issued and outstanding, and entitled to vote. Such request shall state the purpose of purposes of the proposed meeting. Business transacted at any special meeting of stockholders shall be limited to the purposes stated in the notice.

SECTION 7. Whenever stockholders are required or permitted to take any action at a meeting, a written notice of the meeting shall be given which notice shall state the place, date and hour of the meeting, and, in the case of a special meeting, the purpose or purposes for which the meeting is called. The written notice of any meeting shall be given to each stockholder entitled to vote at such meeting not less than ten (10) or more than sixty (60) days before the date of the meeting. If mailed, notice is given when deposited in the United States mail, postage prepaid, directed to the stockholder at his address as it appears on the records of the Corporation.

SECTION 8. The officer who has charge of the stock ledger of the Corporation shall prepare and make, at least ten (10) days before every meeting of stockholders, a complete list of the stockholders entitled to vote at the meeting, arranged in alphabetical order, and showing the address of each stockholder and the number of shares registered in the name of each stockholder. Such list shall be open to the examination of any stockholder, for any purpose germane to the meeting, during ordinary business hours, for a period of at least ten (10) days prior to the meeting, either at a place within the city where the meeting is to be held, which place shall be specified in the notice of the meeting, or, if not so specified, at the place where the meeting is to be held. The list shall also be produced and kept at the time and place of the meeting during the whole time thereof, and may be inspected by any stockholder who is present.

SECTION 9. Unless otherwise provided in the Certificate of Incorporation, any action required to be taken at any annual or special meeting of stockholders of the Corporation, or any action which may be taken at any annual or special meeting of such stockholders, may be taken without a meeting, without prior notice and without a vote, if a consent in writing, setting forth the action so taken, shall be signed by the holders of outstanding stock having not less than the minimum number of votes that would be necessary to authorize or take such action at a meeting at which all shares entitled to vote thereon were present and voted and shall be delivered in a manner consistent with the Delaware General Corporation Law. Prompt notice of the taking of the corporate action without a meeting by less than unanimous written consent shall be given to those stockholders who have not consented in writing.

ARTICLE III

DIRECTORS

SECTION 1. The board of directors shall consist of a minimum of one (1) director and a maximum of seven (7) directors. The number of directors shall be fixed or changed from time to time by an affirmative vote of a majority of the directors then in office. Beginning May 15, 2007, the size of the board shall consist of seven (7) directors. The directors shall be elected at the annual meeting of the stockholders, except as provided in Section 2 of this Article, and each director elected shall hold office until his successor is elected and qualified, provided, however, that unless otherwise restricted by the Certificate of Incorporation or by law, any director or the entire board of directors may be removed, either with or without cause, from the board of directors at any meeting of the stockholders by a majority represented and entitled to vote thereat.

SECTION 2. Vacancies on the board of directors by reason of death, resignation, retirement, disqualification, removal from office, or otherwise, and newly created directorships resulting from any increase in the authorized number of directors may be filled by a majority of the directors then in office, although less than a quorum, or by a sole remaining director. The directors so chosen shall hold office until the next annual election of directors and until their successors are duly elected and shall qualify, unless sooner displaced. If there are no directors in office, then an election of directors may be held in the manner provided by statue. If, at the time of filling any vacancy or any newly created directorship, the directors then in office shall constitute less than a majority of the whole board (as constituted immediately prior to any such increase), the Court of Chancery may, upon application of any stockholder or stockholders holding at least ten percent of the total number of the shares at the time outstanding having the right to vote for such directors, summarily order an election to be held to fill any such vacancies or newly created directorships, or to replace the directors chosen by the directors then in office.

SECTION 3. The property and business of the Corporation shall be managed by or under the direction of its board of directors. In addition to the powers and authorities by these By-Laws expressly conferred upon them, the board may exercise all such powers of the Corporation and do all such lawful acts and things as are not by statute or by the Certificate of Incorporation or by these By-Laws directed or required to be exercised or done by the stockholders.

MEETINGS OF THE BOARD OF DIRECTORS

SECTION 4. The directors may hold their meetings and have one or more offices, and keep the books of the Corporation outside of the State of Delaware.

SECTION 5. The annual meeting of the board of directors shall be held on the first Monday of December immediately following the annual meeting of the stockholders. Regular meetings of the board of directors may be held without notice at such time and place as shall from time to time be determined by the board.

SECTION 6. Special meetings of the board of directors may be called by the president on twenty-four hours’ notice to each director, either personally or by mail or by fax; special meetings shall be called by the president or the secretary in like manner and on like notice on the written request of two directors unless the board consists of only one director; in which case special meetings shall be called by the president or secretary in like manner or on like notice on the written request of the sole director.

SECTION 7. At all meetings of the board of directors a majority of the authorized number of directors shall be necessary and sufficient to constitute a quorum for the transaction of business, and the vote of a majority of the directors present at any meeting at which there is a quorum, shall be the act of the board of directors, except as may be otherwise specifically provided by statue, by the Certificate of Incorporation or by these By-Laws. If a quorum shall not be present at any meeting of the board of directors the directors present thereat may adjourn the meeting from time to time, without notice other than announcement at the meeting, until a quorum shall be present. If only one director is authorized, such sole director shall constitute a quorum.

SECTION 8. Unless otherwise restricted by the Certificate of Incorporation or these By-Laws, any action required or permitted to be taken at any meeting of the board of directors or of any committee thereof may be taken without a meeting, if all members of the board or committee, as the case may be, consent thereto in writing, and the writing or writings are filed with the minutes of proceedings of the board or committee.

SECTION 9. Unless otherwise restricted by the Certificate of Incorporation of these By-Laws, members of the board of directors, or any committee designated by the board of directors, may participate in a meeting of the board of directors, or any committee, by means of conference telephone or similar communication equipment by means of which all persons participating in the meeting can hear each other, and such participation in a meeting shall constitute presence in person at such meeting.

COMMITTEES OF DIRECTORS

SECTION 10. The board of directors may, by resolution passed by a majority of the whole board, designate one or more committees, each such committee to consist of one or more of the directors of the corporation. The board may designate one or more directors as alternate members of any committee, who may replace any absent or disqualified member at any meeting of the committee. In the absence or disqualification of a member of a committee, the member or members thereof present at any meeting and not disqualified from voting, whether or not he or they constitute a quorum, may unanimously appoint another member of the board of directors to act at the meeting in the place of any such absent or disqualified member. Any such committee, to the extent provided in the resolution of the board of directors, shall have and may exercise all the powers and authority of the board of directors in the management of the business and affairs of the Corporation, and may authorize the seal of the Corporation to be affixed to all papers which may require it; but no such committee shall have the power or authority in reference to amending the Certificate of Incorporation (except that a committee may, to the extent authorized in the resolution or resolutions providing for the issuance of shares of stock adopted by the board of directors, fix the designations and any of the preferences or rights of such shares relating to dividends, redemption, dissolution, any distribution of assets of the corporation or the conversion into, or the exchange of such shares for, shares of any other class or classes or any other series of the same or any other class or classes of stock of the corporation or fix the number of shares of any series of stock or authorize the increase or decrease of the shares of any series), adopting an agreement of merger or consolidation, recommending to the stockholders the sale, lease or exchange of all or substantially all of the corporation’s property and assets, recommending to the stockholders a dissolution, or amending the By-Laws of the Corporation; and, unless the resolution, By-Laws, or the Certificate of Incorporation expressly so provide, no such committee shall have the power or authority to declare a dividend, to authorize the issuance of stock, or to adopt a Certificate of Ownership and Merger.

COMPENSATION OF DIRECTORS

SECTION 11. Unless otherwise restricted by the Certificate of Incorporation or these By-Laws, the board of directors shall have the authority to fix the compensation of directors. The directors may be paid their expenses, if any, of attendance at each meeting of the board of directors and may be paid a fixed sum for attendance at each meeting of the board of directors or a stated salary as director. No such payment shall preclude any director from serving the Corporation in any other capacity and receiving compensation therefore. Members of special or standing committees may be allowed like compensation for attending committee meetings.

ARTICLE IV

OFFICERS

SECTION 1. The officers of the Corporation shall be chosen by the board of directors and shall include a President, at least one (1) Secretary and one (1) Treasurer. The Corporation may also have at the discretion of the board of directors such other officers as are desired, including a chairman of the board, chief executive officer, chief operating officer, vice

presidents, one or more assistant secretaries, one or more assistant treasurers and such other officers as may be appointed in accordance with the provisions of Section 3 of this Article IV. In the event there are two or more vice presidents, then one or more may be designated as executive vice presidents, senior vice president, vice president marketing, or other similar or dissimilar title. At the time of the election of officers, the directors may by resolution determine the order of their rank. Any number of offices may be held by the same person, unless the Certificate of Incorporation or these By-Laws otherwise provide.

SECTION 2. The board of directors, at its first meeting and after each annual meeting of the stockholders, shall choose the officers of the Corporation.

SECTION 3. The board of directors may appoint such other officers and agents as it shall deem necessary who shall hold their offices for such terms and shall exercise such powers and perform such duties as shall be determined from time to time by the board of directors.

SECTION 4. The salaries of all officers and agents of the Corporation shall be fixed by the board of directors.

SECTION 5. The officers of the Corporation shall hold office until their successors are chosen and qualify in their stead or until his/her death, resignation or earlier removal. Any officer elected or appointed by the board of directors may be removed at any time, either with or without cause, by the board of directors. If the office of any officer or officers becomes vacant for any reason, the board of directors may fill the vacancy.

PRESIDENT

SECTION 6. The President shall, if present, preside at all meetings of the board of directors and exercise and perform such other powers and duties as may be from time to time assigned to him by the board of directors or prescribed by these By-Laws. The President shall be the principal executive officer of the corporation. Subject to the direction and control of the board of directors, he/she shall be in charge of the business of the corporation; he/she shall see that the resolutions and directions of the board of directors are carried into effect except in those instances in which that responsibility is specifically assigned to some other person by the board of directors; and, in general, he/she shall discharge all duties incident to the office of the President and such other duties as maybe prescribed by the board of directors from time to time. He/she shall preside at all meetings of the shareholders. Except in those instances in which the authority to execute is expressly delegated to another officer or agent of the corporation or a different mode of execution is expressly prescribed by the board of directors or these by-laws, he/she may execute for the Corporation certificates for its shares, and any contracts, deeds, mortgages, bonds or other instruments which the board of directors has authorized to be executed, and he/she may accomplish such execution either under or without the seal of the corporation and either individually or with the secretary, any assistant secretary, or any other officer thereunto authorized by the board of directors, according to the requirements of the form of the instrument. He/she may vote all securities which the corporation is entitled to vote except as and to the extent such authority shall be vested in a different officer or agent of the corporation by the board or directors.

THE VICE-PRESIDENTS

SECTION 7. The Vice-President (or in the event there be more than one Vice-President, each of the Vice-Presidents) shall assist the President in the discharge of his/her duties as from time to time may be assigned to him/her by the President or by the board of directors. In the absence of the President or in the event of his/her inability or refusal to act, the Vice-President, (or in the event there be more than one Vice-President, the Vice-Presidents in the order designated by the board of directors, or by the President if the board of directors has not made such a designation, or in the absence of any designation, then in the order of seniority of tenure as Vice-President) shall perform the duties of the President, and when so acting, shall have the powers of and be subject to all the restrictions upon the President. Except in those instances in which the authority to execute is expressly delegated to another officer or agent of the corporation or a different mode of execution is expressly prescribed by the board of directors or these by-laws, the Vice-President (or each of them if there are more than one) may execute for the corporation certificates for its shares and any contracts, deeds, mortgages, bonds or other instruments which the board of directors has authorized to be executed, and he/she may accomplish such execution either under or without the seal of the corporation and either individually or with the Secretary, any assistant secretary, or any other officer thereunto authorized by the board of directors, according to the requirements of the form of the instrument.

THE TREASURER

SECTION 8. The Treasurer shall be the principal accounting and financial officer of the corporation. He shall: (a) have charge of and be responsible for the maintenance of adequate books of account for the corporation; (b) have charge and custody of all funds and securities of the corporation, and be responsible therefor and for the receipt and disbursement thereof; and (c) perform all the duties incident to the office of the treasurer and such other duties as from time to time may be assigned to him by the chief executive officer or by the board of directors. If required by the board of directors, the Treasurer shall give a bond for the faithful discharge of his duties in such sum and with such surety or sureties as the board of directors may determine.

THE SECRETARY

SECTION 9. The Secretary shall: (a) record the minutes of the shareholders’ and of the board of directors’ meetings in one or more books provided for that purpose; (b) see that all notices are duly given in accordance with the provisions of these by-laws or as required by law; (c) be custodian of the corporate records and of the seal of the corporation; (d) keep a register of the post-office address of each shareholder which shall be furnished to the secretary by such shareholder; (e) sign with the President, or a Vice-President, or any other officer thereunto authorized by the board of directors, certificates for shares of the corporation, the issue of which shall have been authorized by the board of directors, and any contracts, deeds, mortgages, bonds, or other instruments which the board of directors has authorized to be executed, according to the requirements of the form of the instrument, except when a different mode of execution is expressly prescribed by the board of directors or these by-laws; (f) have general charge of the stock transfer books of the corporation; (g) have authority to certify the by-laws, resolutions of the shareholders and board of directors and committees thereof, and other documents of the

corporation as true and correct copies thereof, and (h) perform all duties incident to the office of secretary and such other duties as from time to time may be assigned to him/her by the President or by the board of directors. In the absence of the President and Vice President or in the event of his/her inability or refusal to act, the secretary shall perform the duties of the President, and when so acting, shall have the powers of and be subject to all the restrictions upon the President.

ASSISTANT TREASURERS AND ASSISTANT SECRETARIES

SECTION 10. The assistant treasurers and assistant secretaries shall perform such duties as shall be assigned to them by the treasurer or the secretary, respectively, or by the chief executive officer or the board of directors. The assistant secretaries may sign with the chief executive officer, the president, or a vice-president, or any other officer thereunto authorized by the board of directors, certificates for shares of the corporation, the issue of which shall have been authorized by the board of directors, any contracts, deeds, mortgages, bonds, or other instruments which the board of directors has authorized to be executed, according to the requirements of the form of the instrument, except when a different mode of execution is expressly prescribed by the board of directors or these by-laws. The assistant treasurers shall respectively, if required by the board of directors, give bonds for the faithful discharge of their duties in such sums and with such sureties as the board of directors shall determine.

ARTICLE V

CERTIFICATES OF STOCK

SECTION 1. Every holder of stock of the Corporation shall be entitled to have a certificate signed by, or in the name of the Corporation by, the president or a vice president, and by the secretary, or an assistant treasurer of the Corporation, certifying the number of shares represented by the certificate owned by such stockholder in the Corporation.

SECTION 2. Any or all of the signatures on the certificate may be a facsimile. In case any officer, transfer agent, or registrar who has signed or whose facsimile signature has been placed upon a certificate shall have ceased to be such officer, transfer agent, or registrar before such certificate is issued, it may be issued by the corporation with the same effect as if he were such officer, transfer agent, or registrar at the date of issue.

SECTION 3. If the Corporation shall be authorized to issue more than one class of stock or more than one series of any class, the powers, designations, preferences and relative, participating, optional or other special rights of each class of stock or series thereof and the qualification, limitations or restrictions of such preferences and/or rights shall be set forth in full or summarized on the face or back of the certificate which the Corporation shall issue to represent such class or series of stock, provided that, except as otherwise provided in Section 202 of the Delaware General Corporation Law, or as such section may hereafter be amended, in lieu of the foregoing requirements, there may be set forth on the face or back of the certificate which the Corporation shall issue to represent such class or series of stock, a statement that the Corporation will furnish without charge to each stockholder who so requests, the powers, designations, preferences and relative, participating, optional or other special rights of each class of stock or series thereof and the qualifications, limitations or restrictions of such preference and/or rights.

LOST, STOLEN OR DESTROYED CERTIFICATES

SECTION 4. The board of directors may direct a new certificate or certificates to be issued in place of any certificate or certificates theretofore issued by the Corporation alleged to have been lost, stolen or destroyed, upon the making of an affidavit of that fact by the person claiming the certificate of stock to be lost, stolen or destroyed. When authorizing such issue of a new certificate or certificates, the board of directors may, in its discretion and as a condition precedent to the issuance thereof, require the owner of such lost, stolen or destroyed certificate or certificates, or his legal representative, to advertise the same in such manner as it shall require and/or to give the corporation a bond in such sum as it may direct as indemnity against any claim that may be made against the corporation with respect to the certificate alleged to have been lost, stolen or destroyed.

SECTION 5. Upon surrender to the Corporation, or the transfer agent of the Corporation, of a certificate for shares duly endorsed or accompanied by proper evidence of succession, assignation or authority to transfer, it shall be the duty of the Corporation to issue a new certificate to the person entitled thereto, cancel the old certificate and record the transaction upon its books.

FIXING RECORD DATE

SECTION 6. In order that the Corporation may determine the stockholders entitled to notice of or to vote at any meeting of the stockholders, or any adjournment thereof, or to express consent to corporate action in writing without a meeting, or entitled to receive payment of any dividend or other distribution or allotment of any rights, or entitled to exercise any rights in respect of any change, conversion or exchange of stock or for the purpose of any other lawful action, the board of directors may fix a record date which shall not be more than sixty nor less than ten days before the date of such meeting, nor more than sixty days prior to any other action. A determination of stockholders of record entitled to notice of or to vote at a meeting of stockholders shall apply to any adjournment of the meeting; provided, however, that the board of directors may fix a new record date for the adjourned meeting.

REGISTERED STOCKHOLDERS

SECTION 7. The Corporation shall be entitled to treat the holder of record of any share or shares of stock as the holder in fact thereof and accordingly shall not be bound to recognize any equitable or other claim or interest in such share on the part of any other person, whether or not it shall have express or other notice thereof, save as expressly provided by the laws of the State of Delaware.

ARTICLE VI

GENERAL PROVISIONS

DIVIDENDS

SECTION 1. Dividends upon the capital stock of the Corporation, subject to the provisions of the Certificate of Incorporation, if any, may be declared by the board of directors at any regular or special meeting, pursuant to law. Dividends may be paid in cash, in property, or in shares of the capital stock, subject to the provisions of the Certificate of Incorporation.

SECTION 2. Before payment of any dividend there may be set aside out of any funds of the Corporation available for dividends such sum or sums as the directors from time to time in their absolute discretion, think proper as a reserve fund to meet contingencies, or for equalizing dividends, or for repairing or maintaining any property of the Corporation, or for such other purpose as the directors shall think conducive to the interests of the Corporation, and the directors may abolish any such reserve.

CHECKS

SECTION 3. Such officer or officers as the board of directors may from time to time designate shall sign all checks or demands for money and notes of the Corporation.

FISCAL YEAR

SECTION 4. The fiscal year of the Corporation shall be the calendar year.

CORPORATE SEAL

SECTION 5. The board of directors may provide for a corporate seal which shall have inscribed thereon the name of the corporation and the words “Corporate Seal, Delaware”, said seal may be used by causing it or a facsimile thereof to be impressed or affixed reproduced or otherwise.

NOTICES

SECTION 6. Whenever, under the provisions of the statutes or of the Certificate of Incorporation or of these By-Laws, notice is required to be given to any director or stockholder, it shall not be construed to mean personal notice, but such notice may be given in writing, by mail, addressed to such director or stockholder, at his/her address as it appears on the records of the Corporation, with postage thereon prepaid, and such notice shall be deemed to be given at the time when the same shall be deposited in the United States mail. Notice to directors may also be given by telegram or by overnight express mail.

SECTION 7. Whenever any notice is required to be given under the provisions of the statutes or of the Certificate of Incorporation or of these By-Laws, a waiver thereof in writing, signed by the person or persons entitled to said notice, whether before or after the time stated therein, shall be deemed equivalent thereto.

INDEMNIFICATION

SECTION 8. Unless otherwise provided in the Certificate of Incorporation, the Corporation shall indemnify its officers, directors, employees and agents to the fullest extent permitted by law.

ARTICLE VII

AMENDMENTS

SECTION 1. These By-Laws may be altered, amended or repealed or new By-Laws may be adopted by the stockholders or by the board of directors, when such power is conferred upon the board of by the Certificate of Incorporation, at any regular meeting of the stockholders or of the board of directors or at any special meeting of the stockholders or of the board of directors if notice of such alteration, amendment, repeal or adoption of new By-Laws be contained in the notice of such special meeting. If the power to adopt, amend or repeal these By-Laws is conferred upon the board of directors by the Certificate of Incorporation it shall not divest or limit the power of the stockholders to adopt, amend or repeal these By-Laws.