Inclusion:  Are between the ages of 18 and 65 years old. Are fluent in speaking and reading English. Are able to swallow pills. Agree to have study visits recorded, including Experimental Sessions, assessments, and non-drug psychotherapy sessions. Must provide a contact (relative, spouse, close friend or other support person) 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 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. Agree to the necessary lifestyle modifications. Able to identify support person who can stay with participant overnight after experimental sessions. Suitable home environments to allow completion of all study procedures, including sufficient privacy and access to computer or mobile device with internet access. At Screening, meet DSM-5 criteria for current SAD, generalized subtype At Screening, may have well-controlled hypertension that has been successfully treated with anti-hypertensive medicines, if they pass additional screening to rule out underlying cardiovascular disease At Screening, may have asymptomatic hepatitis C virus (HCV) that has previously undergone evaluation and treatment as needed At Enrollment confirmation for those in delayed treatment group, continue to meet criteria for SAD, generalized subtype Enrollment is allowed with glaucoma only with the approval of their ophthalmologist  Exclusion:  Are not able to give adequate informed consent. Are currently engaged in compensation litigation whereby financial gain would be achieved from prolonged symptoms of SAD or any other psychiatric disorder. Are likely, in the investigator's opinion and via observation during the Preparatory Period, to lack social support or lack a stable living situation or supportive family/network. Have any current problem which, in the opinion of the investigator or Study Physician, might interfere with participation. Would present a serious risk to others as assessed by investigator, Study Physician, or study team. Require certain excluded medications. Have evidence or history of significant (controlled or uncontrolled) hematological, endocrine, cerebrovascular, cardiovascular, coronary, pulmonary, renal, gastrointestinal, immunocompromising, or neurological disease, including seizure disorder, or any other medical disorder judged by the investigator to significantly increase the risk of MDMA administration (participants with hypothyroidism who are on adequate and stable thyroid replacement will not be excluded). Have uncontrolled hypertension using the standard criteria of the American Heart Association (values of 140/90 millimeters of Mercury [mmHg] or higher assessed on three separate occasions). Have a marked baseline prolongation of QT/QTc interval. 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. Have history of hyponatremia or hyperthermia. Weigh less than 48 kilograms (kg). Are pregnant, nursing, or are able to become pregnant and are not practicing an effective means of birth control.  Some eligibility criteria have been omitted to protect the integrity of the recruitment process. Full exclusion/inclusion criteria will be reported with results when recruitment is complete. In the interim, please contact research team to inquire about full inclusion/exclusion criteria.