Safety, Therapeutic Potential, and Mechanisms of Two Psilocybin Doses, Administered With Psychological Support in Young Adults With Anorexia Nervosa

Inclusion Criteria: * Diagnosis of AN per DSM-5, including anorexia nervosa in partial remission. * Have experienced at least one period of weight restoration to a minimum BMI of 17 followed by subsequent weight loss. * Age 16-35 * BMI \>16 * Stable contact with a psychiatric unit * Ability to provide informed consent Exclusion Criteria: * Psychosis, bipolar disorder, substance use disorder, family history of psychosis or bipolar disorder, refusal of birth control, lifetime psychedelic use. * Cardiovascular conditions * Resting systolic blood pressure \>140 mmHg or diastolic blood pressure \>90 mmHg at screening or baseline * Clinically significant arrhythmias, tachycardia and QT prolongation * History of stroke, myocardial infarction, or other significant cardiovascular events * Seizure disorders or history of epilepsy * Diabetes mellitus, positive drug tests, suicidal intent, allergy or intolerance to drug content, blood or needle phobia * Only for the MRI-part of the study: Metal pieces in the body (contraindicated by fMRI, assessed in each case by MR-technician). Non-compliance to fMRI will not lead to study exclusion * Any other clinically significant medical condition that, in the investigator's opinion, may pose a risk to the participant or interfere with study results * Care under the Swedish Compulsory Psychiatric Care Act (LPT) * Ongoing treatment with medications that have clinically relevant 5-HT2A-receptor antagonistic properties and are therefore expected to directly block or substantially interfere with the pharmacodynamic effects of psilocybin. Such medications require an appropriate washout period prior to psilocybin administration, based on pharmacokinetic properties and clinical judgement. Medications without direct 5-HT2A-antagonistic effects are not excluded on this basis. * BMI \> 21.0 for ≥ 6 consecutive months within the 12 months prior to screening, as documented in medical records.