WASHINGTON — Federal health regulators on Friday declined to approve the psychedelic drug MDMA as a therapy for PTSD, a major setback for groups seeking a breakthrough decision in favor of using mind-altering substances to treat serious mental health conditions. Drugmaker Lykos Therapeutics said the FDA notified the company that its drug “could not be approved based on data submitted to date,” and requested an additional late-stage study. Such studies generally takes several years and millions of dollars to conduct.

The company said it plans to ask the agency to reconsider. Lykos and other psychedelic companies had hoped that MDMA would be approved and pave the way for other hallucinogenic drugs to enter the medical mainstream. If the FDA had granted the request, MDMA, also known as ecstasy or molly, would have become the first illegal psychedelic to become a federally approved medicine.

The FDA’s decision was expected after a panel of government advisors voted overwhelmingly against the drug’s use for post-traumatic stress disorder in June. The negative vote came after an all-day meeting in which experts scrutinized Lykos’ study data, research methods and possible risks of the drug, including heart problems, injury and abuse. FDA said Friday the MDMA application had “significant limitations” that “prevent the agency from concluding that the drug is safe and effective for the proposed indication.

” The agency said it will continue encouraging “innovation .