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.