This multi-site open-label study assesses the efficacy and safety of 3,4-methylenedioxymethamphetamine (MDMA)-assisted psychotherapy in participants who were enrolled in a parent study for treatment of posttraumatic stress disorder (PTSD). On February 12, 2021, the Institutional Review Board (IRB) in the United States received the protocol submission for our multi-site open-label study assessing the efficacy and safety of MDMA-assisted therapy in participants diagnosed with at least severe posttraumatic stress disorder (PTSD). On the same day, the Canadian IRB approved the protocol submission for the study site in Montreal. The study has been reviewed by the US FDA and Health Canda and cleared as safe to proceed. The study will be conducted in up to 100 participants. Participants in the two parent Phase 3 trials of MDMA-assisted psychotherapy who did not receive MDMA and who meet all other entry criteria will be eligible and invited to participate in this open-label safety extension study. Participants who are eligible for this study will be contacted by the study site when the site is enrolling.