Effects of Psilocybin in Anorexia Nervosa

General Inclusion Criteria: * Currently meet criteria for AN restricting subtype by Diagnostic and Statistical Manual 5th edition (DSM-5) criteria, and have a history of AN for at least 3 years prior to screening * Have at least one prior attempt at treatment * Be otherwise medically stable as determined by screening for medical problems via a personal interview, a medical questionnaire, a physical examination, an electrocardiogram (ECG), and routine medical blood and urinalysis laboratory tests (complete blood count, comprehensive metabolic panel, urine pregnancy test, urine toxicology screen). * Agree to refrain from using any psychoactive drugs, including alcoholic beverages and nicotine, within 24 hours of each drug administration. The exception is caffeine. General Exclusion Criteria: * Women who are pregnant (as indicated by a positive urine pregnancy test assessed at intake and before each drug session) or nursing; women who are of childbearing potential and sexually active who are not practicing an effective means of birth control. * Cardiovascular conditions: coronary artery disease, stroke, angina, uncontrolled hypertension, a clinically significant ECG abnormality, heart valve, or transient ischemic attack in the past year. Resting heart rate may be no less than 50 beats per minute unless cleared by a cardiologist. * Epilepsy with history of seizures * Type 1 diabetes * First degree relative with schizophrenia spectrum or other psychotic disorders (except substance/medication-induced or due to another medical condition), or Bipolar I Disorder * Has a psychiatric condition judged to be incompatible with establishment of rapport or safe exposure to psilocybin