Unveiling of Lykos CRL triggers a new era of FDA-enforced responsibility
The U.S. Food and Drug Administration (FDA) published 89 Complete Response Letters (CRLs) on September 4, 2025, one of which was for Lykos' application for MDMA-assisted therapy for post-traumatic stress disorder (PTSD). The rejection of the therapy, issued in August 2024, has had significant consequences for the company and the field of psychedelic medicine.
In 2014, the Multidisciplinary Association for Psychedelic Studies (MAPS) created a public benefit corporation named Lykos Therapeutics to move a MDMA-assisted therapy program through late-stage development and regulatory submission. MAPS describes itself as having "incubated" Lykos, while Lykos has carried the responsibility for regulatory filings and fundraising.
The FDA's concerns over safety reporting, trial durability, and blinding in Lykos' trials are now visible to the public. These issues were raised during a meeting of the FDA's Psychopharmacologic Drugs Advisory Committee in June 2024, where the panel voted against the idea that the data provided "substantial evidence of effectiveness." The benefits, they concluded, did not outweigh the risks.
The FDA's detailed reasoning for the rejection of Lykos' therapy is now publicly available. The agency maintains that the evidence provided was not sufficient to establish long-term efficacy or fully characterize safety. One of the concerns included instructions given to trial sites not to record certain euphoria-like effects as adverse events.
The rejection led to Lykos cutting 75% of its staff. However, the company acknowledged the decision and stated they would work diligently to address the FDA's concerns. Lykos has since rebranded itself as Resilient Pharmaceuticals.
The publication of the Lykos CRL allows for a broader public discussion about the FDA's reasoning and the development of the field of psychedelic medicine. MAPS criticized the FDA's content of the CRL, accusing the agency of "moving the goalposts" on trial standards.
In 2017, the FDA granted the program Breakthrough Therapy Designation and reached a Special Protocol Assessment agreement on the design of two pivotal phase 3 trials, known as MAPP1 and MAPP2. These studies reported positive results with improvements on standard PTSD measures among patients receiving MDMA-assisted therapy compared with placebo.
Despite the setback, the field of psychedelic medicine continues to make strides. The rejection of Lykos' therapy does not necessarily signal the end of MDMA-assisted therapy for PTSD, but rather a call for more rigorous and transparent research. As the public and researchers continue to engage in dialogue with the FDA, we can expect to see further developments in this promising area of medicine.
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