Description of Organization and Business Operations	12 Months Ended
Dec. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of Organization and Business Operations	NOTE 1. DESCRIPTION OF ORGANIZATION AND BUSINESS OPERATIONS Acumen Pharmaceuticals, Inc. (“Acumen” or the “Company”) was incorporated in 1996 in the state of Delaware. Acumen discovers and develops targeted therapies for the treatment of Alzheimer’s disease (“AD”). Acumen’s sole drug candidate, ACU193, is a humanized monoclonal antibody which selectively targets amyloid-beta oligomers (“AßOs”). Acumen and Merck & Co., Inc. discovered and developed ACU193 through an eight-year research collaboration. Acumen currently holds exclusive rights to the program. The Company submitted an Investigational New Drug Application for ACU193 to the Food and Drug Administration in the fourth quarter of 2020. The Company initiated a Phase 1 clinical trial of ACU193 in the second quarter of 2021, which the Company named “INTERCEPT-AD.” Approximately 62 individuals with early AD (mild cognitive impairment or mild dementia due to AD) are expected to be randomized into this double-blind, placebo-controlled, first-in-human study of ACU193. INTERCEPT-AD consists of single-ascending-dose and multiple-ascending-dose cohorts and the overall objective of the trial is to evaluate the safety and tolerability and establish clinical proof of mechanism of ACU193 administered intravenously. In October 2021, the Company announced the initial dosing of the first patient in the INTERCEPT-AD trial and the subsequent successful sentinel safety review of the first two patients. Clinical trial site activation and patient recruitment and enrollment is ongoing. At present, INTERCEPT-AD is in the single-ascending-dose portion of the trial. Based on current site activations and enrollment rates, the Company anticipates reporting its topline data from this trial in the first half of 2023. The Company is subject to the uncertainty of whether the Company’s intellectual property will develop into successful commercial products. November 2020 Reverse Stock Split On November 20, 2020, the Company effected a 1-for-30 reverse stock split of its authorized, issued and outstanding shares of common stock and convertible preferred stock. Accordingly, all share and per share amounts for the periods presented in the accompanying financial statements and these notes have been adjusted retroactively, where applicable, to reflect this reverse stock split. On November 20, 2020, the Company also increased the number of shares of preferred stock and common stock authorized for issuance (see Note 6). June 2021 Reverse Stock Split The Company’s Board of Directors (“Board”) approved a reverse split of shares of the Company’s common stock and convertible preferred stock on a 1-for-1.49 basis (the “June 2021 Reverse Stock Split”), which was effected on June 23, 2021. The par value and the number of authorized shares of the convertible preferred stock and common stock were not adjusted in connection with the June 2021 Reverse Stock Split. All references to common stock, convertible preferred stock, warrants to purchase common stock, warrants to purchase convertible preferred stock, options to purchase common stock, share data, per share data and related information contained in the financial statements have been retrospectively adjusted to reflect the effect of the June 2021 Reverse Stock Split for all periods presented. No fractional shares of the Company’s common stock were issued in connection with the June 2021 Reverse Stock Split. Any fractional share resulting from the June 2021 Reverse Stock Split was rounded down to the nearest whole share, and any stockholder entitled to a fractional share as a result of the June 2021 Reverse Stock Split received a cash payment in lieu of receiving fractional shares. Initial Public Offering On July 6, 2021, the Company issued 9,999,999 shares of common stock in an initial public offering (“IPO”), and on July 8, 2021, the Company issued an additional 1,499,999 shares of common stock that were purchased by the underwriters pursuant to the underwriters’ option to purchase additional shares at the public offering price less underwriting discounts and commissions. The price to the public for each share was $16.00. The aggregate net proceeds from the Company’s IPO, after underwriting discounts and commissions and other offering expenses of $15.4 million, were $168.6 million. On July 6, 2021, in connection with the closing of the IPO, 477,297 shares of Series A, 7,985,305 shares of Series A-1, and 19,770,070 shares of Series B convertible preferred stock, respectively, automatically converted into an equal number of shares of common stock. Warrants to purchase shares of common stock were automatically net exercised for the purchase of an aggregate of 178,847 shares of common stock. As a result of the IPO, the underwriters’ exercise of their option, the conversions of the Series A, A-1 and B convertible preferred stock, and the exercise of the warrants, the Company’s total number of outstanding common shares increased by 39,911,517 immediately following the closing of the IPO. Liquidity and Capital Resources The Company has incurred operating losses since inception and expects to continue to incur significant operating losses for the foreseeable future and may never become profitable. As of December 31, 2021 and 2020, the Company had an accumulated deficit of $127.6 million and $27.0 million, respectively, and working capital of $193.5 million and $38.1 million, respectively. Prior to the IPO, the Company historically relied on raising capital from venture capital firms and private investors and funding from a government grant to finance its operations. On June 9, 2021, the Board and the holders of more than 67% of the then outstanding shares of Series B convertible preferred stock held by the Series B purchasers (the “Requisite Investors”) elected to waive the achievement of the milestone subject to the terms and conditions of the Series B Preferred Stock Purchase Agreement (the “Series B Agreement”) and consummate the subsequent closing (the “Milestone Closing”) (see Note 5). On June 17, 2021, the Milestone Closing for the Series B convertible preferred stock occurred, resulting in the sale of 7,908,027 shares of Series B convertible preferred stock at $3.80 per share for gross proceeds of $30.0 million. As a result of the Milestone Closing and the closing of the Company’s IPO on July 6, 2021, management believes that its existing cash and cash equivalents and marketable securities will be sufficient to enable the Company to fund its operating expenses and capital expenditure requirements at least through 202 5 . Future capital requirements will depend upon many factors, including the timing and extent of spending on research and development and market acceptance of the Company’s products. The Company may need to obtain additional financing to complete clinical trials and launch and commercialize any product candidates for which it receives regulatory approval. Until such time, if ever, the Company can generate revenue sufficient to achieve profitability, the Company expects to finance its operations through a combination of equity offerings, debt financings, collaborations, strategic alliances and licensing arrangements. There can be no assurance that such financing will be available on terms acceptable to the Company, or at all. To the extent that the Company raises additional capital through the sale of equity or convertible debt securities, the ownership interest of its stockholders will be diluted, and the terms of these securities may include liquidation of other preferences that adversely affect the rights of common stockholders. Debt financing and preferred equity financing, if available, may involve agreements that include covenants limiting or restricting the Company’s ability to take specific actions, such as incurring additional debt, making acquisitions or capital expenditures or declaring dividends. If the Company is unable to maintain sufficient financial resources, its business, financial condition and results of operations will be materially and adversely affected. The Company may be required to delay, limit, reduce or terminate its product discovery and development activities or future commercialization efforts. In October 2021, the Company announced the initial dosing of the first patient in the INTERCEPT-AD trial and the subsequent successful sentinel safety review of the first two patients. Due to delays in clinical trial site activation and patient enrollment that the Company believes are principally related to effects of the coronavirus (“COVID-19”) pandemic, the Company is expanding the anticipated number of trial sites to support its enrollment objectives and anticipated timelines. Clinical trial site activation and patient recruitment and enrollment is ongoing. At present, INTERCEPT-AD is in the single-ascending-dose portion of the trial. Based on current site activations and enrollment rates, the Company anticipates reporting its topline data from this trial in the first half of 2023. The ultimate impact of the COVID-19 pandemic on the Company’s business, results of operations, financial position and cash flows will depend on future developments, including the duration and spread of the outbreak and related advisories and restrictions. These developments and the impact of the COVID-19 pandemic on the financial markets and the overall economy are highly uncertain and cannot be predicted. If the financial markets and/or the overall economy are impacted for an extended period, the Company’s business, results of operations, financial position and cash flows may be materially adversely affected.

Acumen Pharmaceuticals, Inc. (“Acumen” or the “Company”) was incorporated in 1996 in the state of Delaware. Acumen discovers and develops targeted therapies for the treatment of Alzheimer’s disease (“AD”). Acumen’s sole drug candidate, ACU193, is a humanized monoclonal antibody which selectively targets amyloid-beta oligomers (“AßOs”). Acumen and Merck & Co., Inc. discovered and developed ACU193 through an eight-year research collaboration. Acumen currently holds exclusive rights to the program. The Company submitted an Investigational New Drug Application for ACU193 to the Food and Drug Administration in the fourth quarter of 2020. The Company initiated a Phase 1 clinical trial of ACU193 in the second quarter of 2021, which the Company named

“INTERCEPT-AD.”

Approximately 62 individuals with early AD (mild cognitive impairment or mild dementia due to AD) are expected to be randomized into this double-blind, placebo-controlled,

first-in-human

study of ACU193.

INTERCEPT-AD

consists of single-ascending-dose and multiple-ascending-dose cohorts and the overall objective of the trial is to evaluate the safety and tolerability

and

establish clinical proof of mechanism of ACU193 administered intravenously. In October 2021, the Company announced the initial dosing of the first patient in the

INTERCEPT-AD

trial and the subsequent successful sentinel safety review of the first two patients. Clinical trial site activation and patient recruitment and enrollment is ongoing. At present, INTERCEPT-AD is in the single-ascending-dose portion of the trial. Based on current site activations and enrollment rates, the Company anticipates reporting its topline data from this trial in the first half of 2023.

The Company is subject to the uncertainty of whether the Company’s intellectual property will develop into successful commercial products.

November 2020 Reverse Stock Split

On November 20, 2020, the Company effected a

1-for-30

reverse stock split of its authorized, issued and outstanding shares of common stock and convertible preferred stock. Accordingly, all share and per share amounts for the periods presented in the accompanying financial statements and these notes have been adjusted retroactively, where applicable, to reflect this reverse stock split. On November 20, 2020, the Company also increased the number of shares of preferred stock and common stock authorized for issuance (see Note 6).

June 2021 Reverse Stock Split

The Company’s Board of Directors (“Board”) approved a reverse split of shares of the Company’s common stock and convertible preferred stock on a

1-for-1.49

basis (the “June 2021 Reverse Stock Split”), which was effected on June 23, 2021. The par value and the number of authorized shares of the convertible preferred stock and common stock were not adjusted in connection with the June 2021 Reverse Stock Split. All references to common stock, convertible preferred stock, warrants to purchase common stock, warrants to purchase convertible preferred stock, options to purchase common stock, share data, per share data and related information contained in the financial statements have been retrospectively adjusted to reflect the effect of the June 2021 Reverse Stock Split for all periods presented. No fractional shares of the Company’s common stock were issued in connection with the June 2021 Reverse Stock Split. Any fractional share resulting from the June 2021 Reverse Stock Split was rounded down to the nearest whole share, and any stockholder entitled to a fractional share as a result of the June 2021 Reverse Stock Split received a cash payment in lieu of receiving fractional shares.

Initial Public Offering

On July 6, 2021, the Company issued 9,999,999 shares of common stock in an initial public offering (“IPO”), and on July 8, 2021, the Company issued an additional 1,499,999 shares of common stock that were purchased by the underwriters pursuant to the underwriters’ option to purchase additional shares at the public offering price

less underwriting discounts and commissions. The price to the public for each share was $16.00. The aggregate net proceeds from the Company’s IPO, after underwriting discounts and commissions and other offering expenses of $15.4 million, were $168.6 million.

On July 6, 2021, in connection with the closing of the IPO, 477,297 shares of Series A, 7,985,305 shares of Series

A-1,

and 19,770,070 shares of Series B convertible preferred stock, respectively, automatically converted into an equal number of shares of common stock. Warrants to purchase shares of common stock were automatically net exercised for the purchase of an aggregate of 178,847 shares of common stock.

As a result of the IPO, the underwriters’ exercise of their option, the conversions of the Series A,

A-1

and B convertible preferred stock, and the exercise of the warrants, the Company’s total number of outstanding common shares increased by 39,911,517 immediately following the closing of the IPO.

Liquidity and Capital Resources

The Company has incurred operating losses since inception and expects to continue to incur significant operating losses for the foreseeable future and may never become profitable. As of December 31, 2021 and 2020, the Company had an accumulated deficit of $127.6 million and $27.0 million, respectively, and working capital of $193.5 million and $38.1 million, respectively. Prior to the IPO, the Company historically relied on raising capital from venture capital firms and private investors and funding from a government grant to finance its operations.

On June 9, 2021, the Board and the holders of more than 67% of the then outstanding shares of Series B convertible preferred stock held by the Series B purchasers (the “Requisite Investors”) elected to waive the achievement of the milestone subject to the terms and conditions of the Series B Preferred Stock Purchase Agreement (the “Series B Agreement”) and consummate the subsequent closing (the “Milestone Closing”) (see Note 5). On June 17, 2021, the Milestone Closing for the Series B convertible preferred stock occurred, resulting in the sale of 7,908,027 shares of Series B convertible preferred stock at $3.80 per share for gross proceeds of $30.0 million.

As a result of the Milestone Closing and the closing of the Company’s IPO on July 6, 2021, management believes that its existing cash and cash equivalents and marketable securities will be sufficient to enable the Company to fund its operating expenses and capital expenditure requirements at least through 202

. Future capital requirements will depend upon many factors, including the timing and extent of spending on research and development and market acceptance of the Company’s products. The Company may need to obtain additional financing to complete clinical trials and launch and commercialize any product candidates for which it receives regulatory approval. Until such time, if ever, the Company can generate revenue sufficient to achieve profitability, the Company expects to finance its operations through a combination of equity offerings, debt financings, collaborations, strategic alliances and licensing arrangements. There can be no assurance that such financing will be available on terms acceptable to the Company, or at all. To the extent that the Company raises additional capital through the sale of equity or convertible debt securities, the ownership interest of its stockholders will be diluted, and the terms of these securities may include liquidation of other preferences that adversely affect the rights of common stockholders. Debt financing and preferred equity financing, if available, may involve agreements that include covenants limiting or restricting the Company’s ability to take specific actions, such as incurring additional debt, making acquisitions or capital expenditures or declaring dividends. If the Company is unable to maintain sufficient financial resources, its business, financial condition and results of operations will be materially and adversely affected. The Company may be required to delay, limit, reduce or terminate its product discovery and development activities or future commercialization efforts.

In October 2021, the Company announced the initial dosing of the first patient in the

INTERCEPT-AD

trial and the subsequent successful sentinel safety review of the first two patients. Due to delays in clinical trial site activation and patient enrollment that the Company believes are principally related to effects of the coronavirus (“COVID-19”) pandemic, the Company is expanding the anticipated number of trial sites to support its enrollment objectives and anticipated timelines. Clinical trial site activation and patient recruitment and enrollment is ongoing. At present, INTERCEPT-AD is in the single-ascending-dose portion of the trial. Based on current site activations and enrollment rates, the Company anticipates reporting its topline data from this trial in the first half of 2023. The ultimate impact of the

COVID-19

pandemic on the Company’s business, results of operations, financial position and cash flows will depend on future developments, including the duration and spread of the outbreak and related advisories and restrictions. These developments and the impact of the

COVID-19

pandemic on the financial markets and the overall economy are highly uncertain and cannot be predicted. If the financial markets and/or the overall economy are impacted for an extended period, the Company’s business, results of operations, financial position and cash flows may be materially adversely affected.