As filed with the Securities and Exchange Commission on March 3, 2026

Registration No. 333-   

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM S-8

REGISTRATION STATEMENT

Under

The Securities Act of 1933

AMYLYX PHARMACEUTICALS, INC.

(Exact name of registrant as specified in its charter)

55 Cambridge Parkway, Suite 6W

Cambridge, MA 02142

(617) 682-0917

(Address, including zip code and telephone number, including area code, of Registrant’s principal executive offices)

Amylyx Pharmaceuticals, Inc. 2022 Stock Option and Incentive Plan

Amylyx Pharmaceuticals, Inc. 2022 Employee Stock Purchase Plan

(Full title of the plans)

Joshua B. Cohen, Co-Chief Executive Officer

Justin B. Klee, Co-Chief Executive Officer

Amylyx Pharmaceuticals, Inc.

55 Cambridge Parkway, Suite 6W

Cambridge, MA 02142

(617) 682-0917

(Name, address, including zip code, and telephone number, including area code, of agent for service)

Copies to:

Benjamin K. Marsh, Esq.

Marishka DeToy, Esq.

Goodwin Procter LLP

100 Northern Avenue

Boston, MA 02210

(617) 570-1000

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of the Securities Act. ☐

Statement of Incorporation by Reference

This Registration Statement on Form S-8 is filed to register the offer and sale of (i) an additional 5,494,225 shares of the Registrant’s common stock, $0.0001 par value per share (the “Common Stock”), to be issued under the Registrant’s 2022 Stock Option and Incentive Plan and (ii) an additional 1,098,845 shares of Common Stock to be issued under the Registrant’s 2022 Employee Stock Purchase Plan. This Registration Statement incorporates by reference the contents of the registration statements on Form S-8 (File No.  333-262125, File No.  333-270509, File No.  333-277274 and File No.  333-285534) filed by the Registrant on January 12, 2022, March 13, 2023, February 22, 2024 and March 4, 2025, respectively.

Part II

Information Required in the Registration Statement

See the Exhibit Index below for a list of exhibits filed as part of this registration statement on Form S-8, which Exhibit Index is incorporated herein by reference.

EXHIBIT INDEX

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, the registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-8 and has duly caused this registration statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Cambridge, Commonwealth of Massachusetts, on this 3^rd day of March, 2026.

POWER OF ATTORNEY AND SIGNATURES

KNOW ALL PERSONS BY THESE PRESENTS, that each person whose signature appears below constitutes and appoints Joshua Cohen and Justin Klee and each of them, such person’s true and lawful attorneys-in-fact and agents, with full power of substitution and resubstitution for such person and in such person’s name, place and stead, in any and all capacities, to sign any and all amendments (including post-effective amendments) to this Registration Statement on Form S-8, and to file the same, with all exhibits thereto, and all other documents in connection therewith, with the Securities and Exchange Commission, granting unto each said attorney-in-fact and agent full power and authority to do and perform each and every act and thing requisite and necessary to be done in and about the premises, as fully to all intents and purposes as he might or could do in person, hereby ratifying and confirming all that each of said attorney-in-fact or any substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

Pursuant to the requirements of the Securities Act of 1933, this Registration Statement has been signed by the following persons in the capacities and on the date indicated.

Exhibit 5.1

March 3, 2026

Amylyx Pharmaceuticals, Inc.

55 Cambridge Parkway, Suite 6W

Cambridge, MA 02142

We have acted as your counsel in connection with your filing of a Registration Statement on Form S-8 (the “Registration Statement”) pursuant to the Securities Act of 1933, as amended (the “Securities Act”), on or about the date hereof relating to an aggregate of 6,593,070 shares (the “Shares”) of Common Stock, par value $0.0001 per share (“Common Stock”), of Amylyx Pharmaceuticals, Inc., a Delaware corporation (the “Company”), that may be issued pursuant to the Company’s 2022 Stock Option and Incentive Plan and 2022 Employee Stock Purchase Plan (collectively, the “Plans”).

We have reviewed such documents and made such examination of law as we have deemed appropriate to give the opinion set forth below. We have relied, without independent verification, on certificates of public officials and, as to matters of fact material to the opinion set forth below, on certificates of officers of the Company.

For purposes of the opinion set forth below, we have assumed that, at the time Shares are issued, the total number of then unissued Shares, when added to the number of shares of Common Stock issued, subscribed for, or otherwise committed to be issued, does not exceed the number of shares of Common Stock authorized by the Company’s certificate of incorporation.

The opinion set forth below is limited to the Delaware General Corporation Law.

Based on the foregoing, we are of the opinion that the Shares have been duly authorized and, when delivered against payment therefor in accordance with the terms of the Plans, will be validly issued, fully paid and nonassessable.

This opinion letter and the opinion it contains shall be interpreted in accordance with the Core Opinion Principles as published in 74 Business Lawyer 815 (Summer 2019).

We hereby consent to the inclusion of this opinion as Exhibit 5.1 to the Registration Statement. In giving our consent, we do not admit that we are in the category of persons whose consent is required under Section 7 of the Securities Act or the rules and regulations thereunder.

Very truly yours,

/s/ GOODWIN PROCTER LLP 

GOODWIN PROCTER LLP

Exhibit 23.1

CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

We consent to the incorporation by reference in this Registration Statement on Form S-8 of our report dated March 3, 2026, relating to the financial statements of Amylyx Pharmaceuticals, Inc., appearing in the Annual Report on Form 10-K of Amylyx Pharmaceuticals, Inc. for the year ended December 31, 2025.

/s/ Deloitte & Touche LLP

Boston, Massachusetts

March 3, 2026