Inclusion Criteria:
* Were exposed to stressors related to their work in a health care setting or emergency response system
* Are fluent in speaking and reading English.
* Are able to swallow pills.
* Agree to have study visits recorded, including Experimental Sessions, and non-drug therapy sessions.
* Have a contact (relative, spouse, close friend or other Support Person) who is willing and able to be reached by the Sponsor-Investigators in the event of a participant becoming suicidal or unreachable.
* Agree to inform the Sponsor-Investigators within 48 hours of any medical conditions and procedures.
* 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 birth control through 10 days after the last Experimental Session.
* Comply with requirements for fasting and refraining from certain medications prior to Experimental Sessions, not participate in any other interventional clinical trials during the duration of the study, be driven home after Experimental Sessions, and commit to medication dosing, therapy, and study procedures.
Exclusion Criteria:
* Have previously participated in a clinical treatment trial using MDMA.
* Have a past diagnosis of PTSD unrelated to their work in the healthcare or emergency response systems.
* Have received Electroconvulsive Therapy (ECT) within 12 weeks of enrollment.
* Have a history of or a current primary psychotic disorder or bipolar I disorder
* Have a current eating disorder with active purging
* Have current major depressive disorder with psychotic features
* Have a history of any medical condition that could make receiving a sympathomimetic drug harmful because of increases in blood pressure and heart rate
* Have uncontrolled essential hypertension
* Have a history of ventricular arrhythmia at any time, other than premature ventricular contractions (PVCs) in the absence of ischemic heart disease.
* Have Wolff-Parkinson-White syndrome or any other accessory pathway that has not been successfully eliminated by ablation.
* Have a history of arrhythmia, other than premature atrial contractions (PACs) or occasional PVCs in the absence of ischemic heart disease, within 12 months of screening.
* Have a marked Baseline prolongation of QT/QTc interval (e.g., repeated demonstration of a QTc interval \>450 milliseconds \[ms\] in males and \>460 ms in females corrected by Fridericia's formula).
* Have a history of additional risk factors for Torsade de pointes (e.g., heart failure, hypokalemia, family history of Long QT Syndrome).
* Require use of concomitant medications that prolong the QT/QTc interval during Experimental Sessions.
* Have symptomatic liver disease or have significant liver enzyme elevations.
* Have a history of hyponatremia or hyperthermia.
* Weigh less than 48 kilograms (kg).
* Are pregnant or nursing, or able to become pregnant and are not practicing an effective means of birth control.
