Posttraumatic stress disorder (PTSD) is a debilitating mental disorder, that can develop after service in the armed forces. Psychotherapy performed along with MDMA is an innovative form of therapy for posttraumatic stress disorder. This study will follow on the findings of an initial pilot study in a sample largely made up of people whose PTSD did not develop from serving in the military. This study will investigate whether MDMA-assisted psychotherapy is safe and efficacious in a sample of veterans and whether maintaining an effective double-blind can be better addressed by performing a dose comparison study.