Dose Optimization of MDMA-Assisted Therapy for PTSD

Inclusion Criteria: 1. Are a U.S. military veteran at least 18 years old. 2. Are able to provide written, informed consent. 3. Are able to swallow pills. 4. Agree to have study visits recorded, including Experimental Sessions, psychological assessments, and non-drug therapy sessions. 5. Must provide a contact who is willing and able to be reached by the investigators in the event of a participant becoming unwell or unreachable. 6. If able to become pregnant, must have a negative pregnancy test at study entry and prior to each Experimental Session, and must agree to use adequate contraceptive methods. 7. Must have a current PTSD diagnosis at screening and baseline. 8. Must not participate in any other interventional clinical trials for the duration of the study. 9. Must commit to medication dosing, therapy, and all study procedures. Exclusion Criteria: 1. Are not able to give adequate informed consent. 2. Have a history of any medical condition, or any significant clinical finding on screening tests, that could make receiving a sympathomimetic drug harmful. 3. Have uncontrolled hypertension. 4. Have evidence or history of significant medical or psychiatric disorders. 5. Have symptomatic liver disease. 6. Have history of hyponatremia or hyperthermia. 7. Weigh less than 48 kilograms (kg). 8. Unable or unwilling to safely taper off prohibited psychiatric medication. 9. Abusing illegal drugs or alcohol. 10. Have received Electroconvulsive Therapy (ECT) or ketamine therapy within 12 weeks of enrollment. 11. Are pregnant or nursing or are able to become pregnant and are not practicing an effective means of contraception.