The much-anticipated decision has rattled supporters of psychedelic therapies. The drugmaker says it will ask the agency to reconsider.

Advocates are still fighting to get the psychedelic drug approved as a mental health treatment, despite its rejection by the FDA's advisory committee in June. They face an uphill battle.

Psychedelics researchers and investors are still reeling from last week’s no vote for MDMA by a panel of advisers to the FDA.

Clinical trials of MDMA have been promising, but concerns have emerged about the quality of the research. A June hearing scheduled by the Food and Drug Administration is likely to address them.