Psilocybin-Assisted Therapy for Severe Alcohol Use Disorder

Inclusion Criteria: * Male or female patients between 21 and 64 years old, with a BMI between 17.5 and 30 kg/m2 who * Want to stop or decrease their drinking; * Agree to have all psilocybin-assisted therapy sessions (preparation, administration, integration) and semi-structured interviews recorded; * Have a diagnosis of Severe Alcohol Use Disorder (sAUD), according to the DSM-V (6 criteria or more), ascertained using the Mini International Neuropsychiatric Interview (M.I.N.I 7.0.2). * Are not currently receiving any pharmacological treatment for sAUD and are willing to engage in all study requirements (including attending all study visits, preparatory sessions, integration sessions, follow-up sessions, and completing all study evaluations). * Women of childbearing potential must have a negative serum pregnancy test at admission (day 1 +/-2) and a negative urine pregnancy test the day before psilocybin administration (day 19 +/-2). * Women of childbearing potential must be using an effective, established method of contraception from inclusion until four weeks post-hospital discharge (5 weeks post-psilocybin administration). The following methods of contraception, if used properly and used for the duration of the study, are considered reliable: combined (estrogen and progestogen containing) hormonal contraception associated with inhibition of ovulation: - oral, - intravaginal, - transdermal; progestogen-only hormonal contraception associated with inhibition of ovulation: - oral, - injectable, - implantable; intrauterine device (IUD); intrauterine hormone-releasing system (IUS); bilateral tubal occlusion; vasectomised partner (provided that partner is the sole sexual partner of the woman of child-bearing potential trial participant and that the vasectomised partner has received medical assessment of the surgical success; sexual abstinence (only if defined as refraining from heterosexual intercourse during the entire period of risk associated with the study treatments. The reliability of sexual abstinence needs to be evaluated in relation to the duration of the clinical trial and the preferred and usual lifestyle of the subject). Note: female participants who are permanently sterilized (eg hysterectomy and/or bilateral salpingectomy) or post-menopausal (at least 48 consecutive weeks without menstruation) are not considered as being of child bearing potential. * Men with a woman of childbearing potential partner should use a condom from inclusion until four weeks post-hospital discharge (5 weeks post-psilocybin administration). * Good physical health with no unstable medical conditions, as determined by medical history, physical examination, routine blood labs, electrocardiogram, urine analysis, and urine toxicology. * Willing to refrain from consuming psychoactive substances after enrolling in the study and during follow-up. * Ability to provide voluntary written informed consent after receiving written information about the study protocol. * Undergoing a 4-week alcohol detoxification program at the Brugmann University Hospital. * Remaining abstinent from alcohol during the detoxification program (abstinence will be monitored using a breathalyzer during unannounced checks). * Normal level of language comprehension (French). * Affiliation to the Belgian social security system. Exclusion Criteria: * Allergy, hypersensitivity, or other adverse reactions to previous use of psilocybin or other hallucinogens. * Uncorrected hypertension. * Cardiovascular diseases, hepatic diseases, gastroenterological diseases, hematologic diseases, renal diseases, endocrine diseases, metabolic diseases, inflammatory diseases, neurological diseases or any other somatic condition that, in the opinion of the medical investigator (necessarily an M.D.), would pose a risk to the participant's participation in the study. * Other somatic conditions that, in the opinion of the investigator, would pose a risk to the participant's participation in the study. * Decompensated hepatic cirrhosis, defined by Child B or C score. * Serious abnormalities of complete blood count or chemistries, biological abnormalities including TP \< 50%, albumin \< 35 g/L, total bilirubin \> 35 μmol/L, leading to a Child B or C score. * Abnormal ECG. Clinical ECG diagnoses and ECG signs subject to exclusion and needing medical attention: Atrial flutter or fibrillation, AV block 2nd degree or higher, AVNRT (AV-nodal re-entry tachycardia), AVRT (atrioventricular re-entry tachycardia), tri-fascicular block, signs of rare conditions such as Brugada syndrome or Wolff-Parkinson White Syndrome (Delta wave), Epsilon wave, Fusion beats, signs of acute myocardial ischemia such as ST elevation, signs of pulmonary embolism, Long QTc (≥470 ms for males and ≥480 ms for females), Sinus bradycardia \<40bpm, Sinus node dysfunction (Sick sinus syndrome), Sinus node exit block, Supraventricular tachycardia (SVT), Torsades de Pointes, Ventricular fibrillation, Ventricular flutter, Ventricular tachycardia. This list might not be exhaustive and any other anomaly will be thoroughly assessed by the study physician, lead to exclusion if deemed necessary and referred to cardiology if warranted. * Cognitive impairment (Folstein Mini Mental State Exam (Folstein et al., 1975) score \< 26). * Alcohol withdrawal complication(s), seizure, head injury or stroke within the last 6 months. * Current active acute stress disorder/post-traumatic stress disorder, * Lifetime history of schizophrenia spectrum disorders (schizophrenia, schizoaffective disorder, unspecified), other psychotic disorders or bipolar spectrum disorders (Type I, II, unspecified). * Lifetime history of major depressive episode with psychotic features. * Significant risk of suicide according to clinician assessment. * Family history of schizophrenia spectrum disorders (schizophrenia, schizoaffective disorder, unspecified), or other psychotic disorders, or bipolar Type I in first- or second-degree relatives. * Other substance use disorder (except for caffeine, nicotine, or cannabis) according to DSM-V criteria in the two months preceding inclusion to the study. * Severe cannabis use disorder according to the DSM-V. * Need to take medication with significant potential to interact with classical psychedelics (e.g., antidepressants except selective serotonin reuptake inhibitors (SSRIs), antipsychotics, psychostimulants, treatments for alcohol addiction as naltrexone or acamprosate or baclofen, opioid agonist treatment as buprenorphine or methadone, lithium, anticonvulsants, other dopaminergic or serotonergic agents, inhibitors of UGT1A9 and 1A10, monoamine oxidase inhibitors (MAOIs), aldehyde dehydrogenase inhibitors (ALDHs) and alcohol dehydrogenase inhibitors (ADHs)). * High risk of adverse emotional or behavioral reaction based on investigator's clinical evaluation (e.g., evidence of serious personality disorder, antisocial behavior, serious current stressors, lack of meaningful social support). * History of hallucinogen use disorder, or \>25 lifetime uses. * Pregnancy and breastfeeding, at screening visit and till dosing day. * Known or suspected non-compliance. * Previous enrollment into the current study. * Enrollment of the investigator, his/her family members, employees and other dependent persons. * Patient subject to a legal protection measure (guardianship, curatorship or safeguard of justice), patient unable to express consent and not subject to a protection measure. * Patients with language barrier (unable to follow the protocol or respond to clinical assessments).