 This study will look at MDMA-assisted psychotherapy in 12 individuals aged 18 years or older diagnosed with PTSD that arose out of war or terrorism-related trauma, with PTSD symptoms not improving after trying at least one treatment. Eight of 12 participants will be assigned to receive the full dose of MDMA, and four will be assigned to receive a low or active placebo dose of MDMA during each of two experimental sessions. People will be assigned to full or low-dose MDMA by chance, as by flipping a coin. The fully active dose consists of an initial dose of 125 mg MDMA and a supplemental dose of 62.5 mg given 2 to 2.5 hours later. The active placebo dose consists of an initial dose of 25 mg MDMA and a supplemental dose of 12.5 mg. 