RecruitingPhase 2Drug trialMDMA-Assisted Massed Exposure Therapy for PTSDThe goal of this clinical trial is to investigate the efficacy of 3,4-methylenedioxy-methamphetamine hydrochloride (MDMA) combined with Massed Prolonged Exposure (PE) therapy for the treatment of posttraumatic stress disorder (PTSD) in adult participants diagnosed with PTSD. This randomized, placebo-controlled trial will enroll 95 participants. The main questions it aims to answer are: * Does the combination of PE + MDMA lead to greater reduction in PTSD symptom severity from pre-treatment to one-month follow-up compared to PE + placebo? * Does PE + MDMA improve response efficiency and durability of PTSD symptom improvement compared to PE + placebo? * Does MDMA + PE enhance extinction retention and reduce amygdala threat reactivity, and are these changes associated with improved PTSD outcomes? Participants will: * Receive 10 sessions of Massed Prolonged Exposure therapy over two weeks * Be administered either 100 mg of MDMA or a placebo at Visit 2 * Undergo blinded independent evaluator assessments using the Clinician-Administered PTSD Scale for DSM-5-R (CAPS-5-R) at the one-month posttreatment follow-up