Commitments and Contingencies	12 Months Ended
Dec. 31, 2025
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	16. Commitments and Contingencies Letter of Credit Restricted cash equivalents consist of $0.9 million of cash serving as collateral for a letter of credit issued for the Company’s office spaces, and $0.1 million as collateral for a corporate credit card program. As of December 31, 2025 and December 31, 2024, the Company’s restricted cash equivalents balance was $1.0 million and $1.4 million on its consolidated balance sheets, respectively. Legal Proceedings On February 9, 2024, a putative class action lawsuit was filed in the U.S. District Court for the Southern District of New York against us and certain of our current and former officers (Shih v. Amylyx Pharmaceuticals, Inc., et al., Case Number 1:24-CV-00988, or the Shih Complaint). Plaintiff filed an amended complaint on June 24, 2024. The Shih Complaint asserts a claim against all defendants for alleged violations of Section 10(b) of the Exchange Act and Rule 10b-5 promulgated thereunder and a claim under Section 20(a) against certain current and former officers as alleged controlling persons. The Shih Complaint alleges that defendants made materially false and misleading statements related to the commercial results and prospects for RELYVRIO. The Shih Complaint seeks unspecified damages, interest, costs and attorneys’ fees, and other unspecified relief that the court deems appropriate. On August 12, 2024, the case was transferred from the U.S. District Court for the Southern District of New York to the U.S. District Court for the District of Massachusetts, or the Court, and assigned docket number 1:24-CV-12068. Following the transfer, on September 6, 2024, defendants moved to dismiss the Shih Complaint. On September 30, 2025, the Court issued an order finding that the majority of the alleged misstatements are inactionable, but ultimately denied the motion to dismiss. The Company filed an answer on October 30, 2025. The parties have agreed to participate in a confidential mediation, currently scheduled for March 12, 2026, in an attempt to resolve this action, and will provide a status update to the court by April 12, 2026. In addition to the Shih Complaint, on October 2, 2024, a derivative complaint was filed in the U.S. District Court for the District of Massachusetts against certain current and former director and officer defendants, or the Individual Defendants, naming us as a nominal defendant (Jones v. Cohen, et al., 1:24-CV-12527, or the Jones Derivative Complaint). The substantive allegations mirror those of the Shih Complaint but also include claims for alleged violations of Section 14(a) of the Exchange Act, breach of fiduciary duty, insider trading, and unjust enrichment against the Individual Defendants. The Jones Derivative Complaint seeks unspecified damages to be awarded to the Company along with interest, restitution, unspecified corporate governance and internal procedural reforms and improvements, and plaintiff's attorneys' fees and costs. On October 31, 2024, the Court entered an order staying the action until the earlier of the dismissal of the Shih Complaint with prejudice, including the exhaustion of all appeals, or defendants file an answer to the Shih Complaint. On July 2, 2025, a second derivative complaint was filed in the Court against certain current and former directors and officer defendants, naming the Company as nominal defendant (Hassine v. Cohen, et al., 1:25-CV-11879, or the Hassine Derivative Complaint and, together with the Jones Derivative Complaint, the Derivative Complaints). The substantive allegations mirror those of the Shih Complaint but also include claims for alleged violations of Sections 14(a), 10(b), and 21D of the Exchange Act, breach of fiduciary duty, and certain other common law claims. The Hassine Derivative Complaint seeks unspecified damages to be awarded to the Company along with interest, costs, and attorneys’ fees, restitution, and certain corporate governance and internal procedural reforms and improvements. On July 16, 2025, the parties to both Derivative Complaints moved the Court to consolidate the Hassine Derivative Complaint with the Jones Derivative Complaint and stay the action according to the terms of the previously-entered stay of the Jones Derivative Complaint. The Court approved the motion on July 22, 2025. Due to the above-referenced mediation currently scheduled for March 12, 2026, the previously-entered stay has been extended through April 30, 2026, at which point the parties will determine whether to enter a proposed case schedule or further extend the stay. We intend to defend against the Shih Complaint and Derivative Complaints vigorously. At this time, an estimate of the impact, if any, of the claims made in the Shih Complaint and Derivative Complaints cannot be made. Royalty Payments The Company has entered into a limited number of grant and royalty agreements that include payment obligations contingent upon future events, such as commercialization or the receipt of proceeds from revenue-generating transactions related to the underlying technologies. As the conditions that would trigger royalty payments have not been met, no amounts have been recorded in the consolidated financial statements. Purchase Commitments The Company enters into agreements in the normal course of business with CMOs for raw material purchases and manufacturing services. As of December 31, 2025, there are no amounts committed under these agreements.

Commitments and Contingencies

12 Months Ended

Dec. 31, 2025

Commitments and Contingencies Disclosure [Abstract]

16. Commitments and Contingencies

Letter of Credit

Restricted cash equivalents consist of $0.9 million of cash serving as collateral for a letter of credit issued for the Company’s office spaces, and $0.1 million as collateral for a corporate credit card program. As of December 31, 2025 and December 31, 2024, the Company’s restricted cash equivalents balance was $1.0 million and $1.4 million on its consolidated balance sheets, respectively.

Legal Proceedings

On February 9, 2024, a putative class action lawsuit was filed in the U.S. District Court for the Southern District of New York against us and certain of our current and former officers (Shih v. Amylyx Pharmaceuticals, Inc., et al., Case Number 1:24-CV-00988, or the Shih Complaint). Plaintiff filed an amended complaint on June 24, 2024. The Shih Complaint asserts a claim against all defendants for alleged violations of Section 10(b) of the Exchange Act and Rule 10b-5 promulgated thereunder and a claim under Section 20(a) against certain current and former officers as alleged controlling persons. The Shih Complaint alleges that defendants made materially false and misleading statements related to the commercial results and prospects for RELYVRIO. The Shih Complaint seeks unspecified damages, interest, costs and attorneys’ fees, and other unspecified relief that the court deems appropriate. On August 12, 2024, the case was transferred from the U.S. District Court for the Southern District of New York to the U.S. District Court for the District of Massachusetts, or the Court, and assigned docket number 1:24-CV-12068. Following the transfer, on September 6, 2024, defendants moved to dismiss the Shih Complaint. On September 30, 2025, the Court issued an order finding that the majority of the alleged misstatements are inactionable, but ultimately denied the motion to dismiss. The Company filed an answer on October 30, 2025. The parties have agreed to participate in a confidential mediation, currently scheduled for March 12, 2026, in an attempt to resolve this action, and will provide a status update to the court by April 12, 2026.

In addition to the Shih Complaint, on October 2, 2024, a derivative complaint was filed in the U.S. District Court for the District of Massachusetts against certain current and former director and officer defendants, or the Individual Defendants, naming us as a nominal defendant (Jones v. Cohen, et al., 1:24-CV-12527, or the Jones Derivative Complaint). The substantive allegations mirror those of the Shih Complaint but also include claims for alleged violations of Section 14(a) of the Exchange Act, breach of fiduciary duty, insider trading, and unjust enrichment against the Individual Defendants. The Jones Derivative Complaint seeks unspecified damages to be awarded to the Company along with interest, restitution, unspecified corporate governance and internal procedural reforms and improvements, and plaintiff's attorneys' fees and costs. On October 31, 2024, the Court entered an order staying the action until the earlier of the dismissal of the Shih Complaint with prejudice, including the exhaustion of all appeals, or defendants file an answer to the Shih Complaint.

On July 2, 2025, a second derivative complaint was filed in the Court against certain current and former directors and officer defendants, naming the Company as nominal defendant (Hassine v. Cohen, et al., 1:25-CV-11879, or the Hassine Derivative Complaint and, together with the Jones Derivative Complaint, the Derivative Complaints). The substantive allegations mirror those of the Shih Complaint but also include claims for alleged violations of Sections 14(a), 10(b), and 21D of the Exchange Act, breach of fiduciary duty, and certain other common law claims. The Hassine Derivative Complaint seeks unspecified damages to be awarded to the Company along with interest, costs, and attorneys’ fees, restitution, and certain corporate governance and internal procedural reforms and improvements. On July 16, 2025, the parties to both Derivative Complaints moved the Court to consolidate the Hassine Derivative Complaint with the Jones Derivative Complaint and stay the action according to the terms of the previously-entered stay of the Jones Derivative Complaint. The Court approved the motion on July 22, 2025. Due to the above-referenced mediation currently scheduled for March 12, 2026, the previously-entered stay has been extended through April 30, 2026, at which point the parties will determine whether to enter a proposed case schedule or further extend the stay.

We intend to defend against the Shih Complaint and Derivative Complaints vigorously. At this time, an estimate of the impact, if any, of the claims made in the Shih Complaint and Derivative Complaints cannot be made.

Royalty Payments

The Company has entered into a limited number of grant and royalty agreements that include payment obligations contingent upon future events, such as commercialization or the receipt of proceeds from revenue-generating transactions related to the underlying technologies. As the conditions that would trigger royalty payments have not been met, no amounts have been recorded in the consolidated financial statements.

Purchase Commitments

The Company enters into agreements in the normal course of business with CMOs for raw material purchases and manufacturing services. As of December 31, 2025, there are no amounts committed under these agreements.