An advisory panel to the Food and Drug Administration (FDA) on Tuesday rejected a proposal to use the psychedelic substance MDMA as a treatment for post-traumatic stress disorder (PTSD), the Associated Press reports.

The panel voted 10-1 against the overall benefits of MDMA when used to treat PTSD. Their objections included flawed study data, questionable research conduct and significant risks from MDMA. The FDA is not required to follow the panel’s advice, and is expected to make a final decision by August.

Panelists noted a lack of diversity among study participants. Almost all patients studied were white, with only five black patients included in the research. The panelists drew attention to flawed research that could have skewed the results and missing follow-up data on patient outcomes. They also noted allegations of misconduct in the trials, which were outlined in a report by the nonprofit Institute for Clinical and Economic Review.

The panel said it was difficult to objectively test MDMA, because it causes intense, psychological experiences. Almost all of the patients in two key studies were able to guess whether they had received MDMA or a placebo. Panelists also said it was hard to know how much of patients’ improvement came from MDMA or from the extensive therapy they received – totaling more than 80 hours for many patients.