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.