Post-traumatic stress disorder (PTSD) affects millions of people each year, mostly survivors and witnesses of terrifying or shocking events, such as warfare, assaults or disasters. Because existing treatments don’t work for everyone, new therapies are urgently needed. Today, scientists report results and follow-up data from a phase 3 clinical trial of a psychedelic drug, 3,4-methylenedioxymethamphetamine (MDMA), known on the street as “ecstasy” or “molly,” combined with psychotherapy for the treatment of PTSD. Their preliminary data suggest that the therapy works even in hard-to-treat patients, such as those with drug or alcohol use disorders.