MDMA - most commonly known as a party drug - could be more effective than therapy alone at treating post-traumatic stress disorder (PTSD). The results of a keenly-awaited trial suggest two-thirds of people no longer qualified for a PTSD diagnosis after treatment. The study represents a significant step towards approval of the drug in the US. PTSD can be the result of a very distressing or frightening event, or longer-term series of experiences. That might include accidents, abuse, rape, combat or illness. And it can be very difficult to treat. This trial, run by US charity the Multidisciplinary Association for Psychedelic Studies (Maps), found 88% of people had a "meaningful reduction in symptoms" and 67% no longer qualified for a PTSD diagnosis at all after 18 weeks and three sessions of MDMA-assisted therapy. Talking therapy alone led to a significant improvement in 60%, and remission in 32% of people. The participants in the study, which was published in the journal Nature, had suffered from PTSD for an average of 14 years. MDMA appears to work in part by calming the amygdala. In people with PTSD and anxiety disorders, this part of the brain can overreact, sounding the alarm over seemingly small events. When we are babies, and again during adolescence, we experience periods where our brains are very pliable. The scientists involved in the study speculate that psychedelics and similar-acting drugs like MDMA might allow a "reopening" of this critical window of brain development.