A U.S. Food and Drug Administration advisory committee overwhelmingly voted Tuesday that evidence is lacking that MDMA-assisted therapy is effective for treating post-traumatic stress disorder, and that the benefits don’t outweigh the risks to patients, dealing a potential blow to what could be the first psychedelic treatment the agency approves.

The advisory committee is made up of independent mental health and medical experts, and its vote is not binding. Still, its recommendation could hold great weight as the FDA decides for the first time whether the mind-altering compound – better known by its street name, ecstasy, and long categorized among the riskiest of controlled substances – can be legally used as a medical treatment in the United States.