MDMA Assisted Therapy for BN

Inclusion Criteria: Participants will be included in the protocol if they meet the following criteria: * At least 18 years of age * Meet criteria for Bulimia Nervosa as measured by the EDA-5 * Able to provide written, informed consent * Able to swallow pills * Agree to have study visits recorded, including Experimental Sessions and non-medication therapy sessions * Provides 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 * Agrees 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 contraceptive methods through 10 days after the last Experimental Session. Adequate contraceptive methods include intrauterine device (IUD), injected, implanted, intravaginal, or transdermal hormonal methods, abstinence, oral hormones plus a barrier contraception, vasectomized sole partner, or double barrier contraception. Two forms of contraception are required with any barrier method or oral hormones (i.e., condom plus diaphragm, condom or diaphragm plus spermicide, oral hormonal contraceptives plus spermicide or condom). 'Not able to become pregnant' is defined as permanent sterilization, postmenopausal, or assigned male at birth * Agrees to the lifestyle modifications * Live within reasonable driving distance of the study site (equal to or less than an estimated 2-hour drive from the study site). * Have an identified Primary Care Physician (PCP) and provide consent for the investigator to communicate with PCP, as needed. * Current or past treatment were not successful to retain remission (i.e., continued to meet criteria for BN) despite participating in at least one ED-specific episode of treatment (inpatient, residential, partial hospitalization, intensive outpatient), as confirmed by medical records, by a general practitioner, or by a specialist in ED. * Are medically stable according to screening 12-lead Electrocardiogram (ECG), blood pressure monitoring, blood and urine laboratory screening results, and medical history. Exclusion Criteria: Participants will be excluded from participation for the following reasons: * Alanine transaminase (ALT) \[or aspartate transaminase (AST)\] \> 2 x upper limit of normal (ULN). Total bilirubin \> 1.5 x ULN (isolated bilirubin \> 1.5 x ULN is acceptable if total bilirubin is fractionated and direct bilirubin \< 35%). * Estimated glomerular filtration rate (eGFR) less than 60. * Current unstable liver or biliary disease per investigator assessment defined by presence of ascites, encephalopathy, coagulopathy, hypoalbuminemia, esophageal or gastric varices, persistent jaundice, or cirrhosis. Note: Stable chronic liver disease (including Gilbert's syndrome, asymptomatic gallstones, and chronic stable hepatitis B (e.g., the presence of hepatitis B surface antigen or positive hepatitis C antibody test result without evidence of active infection at screening or within 3 months prior to starting study intervention) is acceptable if the participant otherwise meets entry criteria. * Self-induced vomiting of over 14 times per week * Symptomatic Hepatitis C virus (HCV) * Moderate alcohol or cannabis use disorder (meets \> 3 of 11 diagnostic criteria per DSM-5) or moderate alcohol or cannabis use disorder in early remission for the 3 months prior to enrollment (meets 4 or 5 of 11 diagnostic criteria per DSM-5) * Diabetes Type 1 or Unstable Type 2 Diabetes * Untreated hypothyroidism * Are likely, in the investigator's opinion and via observation during the Preparatory Period, to lack social support or a stable living situation * 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; * Have previously participated in a MAPS-sponsored MDMA clinical trial * Have any current problem which, in the opinion of the investigator or study clinician, might interfere with participation * Have hypersensitivity to any ingredient of the IMP (Investigational Medicinal Product) * Have received Electroconvulsive Therapy (ECT) within 12 weeks of enrollment * Have a history of or a current primary psychotic disorder, bipolar disorder 1 assessed via CAT-MH and confirmed via clinical interview or dissociative identity disorder assessed via DDIS and confirmed via clinical interview * Have current major depressive disorder with psychotic features assessed via CAT-MH * Have a current moderate (not in early remission in the 3 months prior to enrollment; meets 4 or 5 of 11 diagnostic criteria per DSM-5) or severe alcohol or cannabis use disorder within the 12 months prior to enrollment (meets at least 6 of 11 diagnostic criteria per DSM-5) * Have an active illicit drug or prescription drug substance use disorder at any severity (other than cannabis) within 12 months prior to enrollment * Any participant presenting current serious suicide risk, as determined through psychiatric interview, responses to C-SSRS, and clinical judgment of the investigator will be excluded; however, history of suicide attempts is not an exclusion. Any participant who is likely to require hospitalization related to suicidal ideation and behavior, in the judgment of the investigator, will not be enrolled. Any participant presenting with the following on the Baseline C-SSRS will be excluded: a. Suicidal ideation score of 4 or greater within the last month of the assessment at a frequency of once a week or more; b. Suicidal ideation score of 5 within the last 6 months of the assessment; c. Any suicidal behavior, including suicide attempts or preparatory acts, within the last 6 months of the assessment. Participants with non-suicidal self-injurious behavior may be included if approved by the study