Efficacy and Safety of COMP360 Psilocybin Therapy in Anorexia Nervosa: a Proof-of-concept Study

Inclusion Criteria: 1. Any sex and aged 18 years or above at screening. 2. Meeting criteria for AN either restrictive or binge-purging type, according to the DSM-5, based on medical records, clinical assessment, BMI, and documented completion of MINI 7.0.2 and EDE at screening. 3. Have successfully discontinued all prohibited medications for a period of at least two weeks prior to baseline. For fluoxetine (Prozac), immediate cessation at screening period visit 1a followed by at least four weeks of washout will be required prior to baseline. 4. Has a history of disordered eating with duration of at least 3 years prior to screening, that is consistent with AN. 5. BMI ≥15 kg/m2 and ≤20 kg/m2. For participants with a BMI \<16 kg/m2 and \>18.5 kg/m2 at screening, approval from the Medical Monitor will be required. Any participant with a BMI \>18.5 kg/m2 must meet all of the criteria for AN except that, despite significant weight loss, the individual's weight is within or above the normal range. 6. Being otherwise medically stable at screening determined by clinical interview, clinical laboratory values, vital signs, ECG, and medical history. 7. Have at least one documented prior attempt at treatment in the past 3 years. Exclusion Criteria: 1. Prior or ongoing bipolar disorder, any psychotic disorder, including schizophrenia, schizophreniform disorder, schizoaffective disorder, brief psychotic disorder (unless substance induced or due to a medical condition), antisocial personality disorder, or any serious psychiatric comorbidity as assessed by medical history and a structured clinical interview (MINI 7.0.2). 2. Prior or ongoing paranoid, schizoid, schizotypal, histrionic, narcissistic personality disorder based on medical history and clinical judgment. 3. Borderline personality disorder as demonstrated by medical history, the MINI Plus - BPD and clinical judgment. 4. Significant suicide risk as defined by (1) suicidal ideation as endorsed on items 4 or 5 on the C-SSRS within the past year, at screening or at baseline, or; (2) suicidal behaviours within the past year or; (3) clinical assessment of significant suicidal risk during participant interview. 5. Current (within last year) alcohol or substance use disorder as informed by the DSM-5 assessed via the MINI 7.0.2, and urine toxicology at screening. 6. Other personal circumstances and behaviour judged to be incompatible with establishment of rapport or safe exposure to psilocybin. 7. Exposure to psilocybin, or any other psychedelics, such as ayahuasca, mescaline, LSD, or peyote within the past year.