 In the first study segment, Stage 1, all participants will have two blinded experimental sessions of MDMA-assisted psychotherapy scheduled at a two to four week interval, within a moderate course of non-drug psychotherapy preparatory and integrative sessions, after which they will complete the primary endpoint assessment. After the primary endpoint assessment, the subject and therapists will be unblinded and fully debriefed. Participants assigned to receive active dose MDMA will then receive a third open-label experimental session with the same active dose of MDMA, which will complete Stage 1. Participants assigned to receive placebo will crossover, without completing Stage 1, to an open-label study segment following similar procedures, referred to as Stage 2. Participants enrolled in this group will receive the same dose of MDMA as the active dose in Stage 1, with an optional supplemental half dose, at each of three experimental sessions at time points equivalent to those in Stage 1. 