Study Comparing Two Versus Three Active MDMA-assisted Sessions in U.S. Military Veterans With Chronic PTSD

Inclusion Criteria: * U.S. military veteran * Are at least 18 years old. * Are fluent in speaking and reading the predominantly used or recognized language of the study site. * Are able to swallow pills. * Agree to have study visits recorded, including Experimental Sessions, Independent Rater assessments, and non-drug psychotherapy sessions. * Must provide a contact (relative, spouse, close friend or other caregiver) who is willing and able to be reached by the investigators in the event of a participant becoming suicidal or unreachable. * Must agree to inform the investigators within 48 hours of any medical conditions and procedures. * If of childbearing potential, must have a negative pregnancy test at study entry and prior to each Experimental Session, and must agree to use adequate birth control through 10 days after the last Experimental Session. * Must not participate in any other interventional clinical trials during the duration of the study. * Must be willing to remain overnight at the study site after each Experimental Session and be driven home after, and commit to medication dosing, therapy, and study procedures. * At baseline, have moderate PTSD diagnosis. Exclusion Criteria: * Are not able to give adequate informed consent. * Have uncontrolled hypertension. * Have a marked baseline prolongation of QT/QTc interval (e.g., repeated demonstration of a QTc interval \>450 milliseconds \[ms\] corrected by Bazett's formula). * Have a history of additional risk factors for Torsade de pointes (e.g., heart failure, hypokalemia, family history of Long QT Syndrome). * Have evidence or history of significant medical disorders. * Have symptomatic liver disease. * Have history of hyponatremia or hyperthermia. * Weigh less than 48 kilograms (kg). * Are pregnant or nursing, or are of childbearing potential and are not practicing an effective means of birth control. * Have used Ecstasy (material represented as containing MDMA) more than 10 times within the last 10 years or at least once within 6 months of the first Experimental Session; or have previously participated in a MAPS-sponsored MDMA clinical trial.