Inclusion Criteria:
* 25-65 years old
* Male
* English fluency
* Meets criteria for DSM-V moderate or severe AUD.
* Have at least 4 heavy drinking days (5 or more standard drinks in a day) in the past 30 days.
* No history of a of cerebrovascular accident, asthma, or significant alcohol withdrawal history
* No seizure disorder, coronary artery disease, heart failure, uncontrolled hypertension, insulin-dependent diabetes
* No current substance use disorder other than AUD
* Negative drug screen (other than THC) on drug administration day
* No prescription medications classified as UGT1A9 inhibitors, UGT1A10 inhibitors, aldehyde or alcohol dehydrogenase inhibitors.
* At least a high-school level of education or equivalent (e.g. GED).
* Lived at current residence for at least 3 months.
* Family member/friend for pick-up, overnight post-drug session monitoring.
* No hallucinogen or ketamine use in past 1 year
* No self-reported, personal, or familial history of specific psychotic disorders/episodes as subjects who take psilocybin may experience a worsening and/or persistent psychotic state. Therefore, these subjects are excluded due to an abundance of caution since even a family history may create a vulnerability to psychosis.
* No serious traumatic brain injury (TBI) in the past 2 years.
* No known allergies to rescue medication (diazepam)
* Weight between 110 and 330 lbs
Exclusion Criteria:
* Drug/medication assessment that yields: nonprescription medication use, nutritional supplement, or herbal supplement (except when approved by the study investigators), medically unstable, current medication use that has significant potential to interact with study drug (e.g., antidepressants, antipsychotics, psychostimulants, treatments for addictions, other dopaminergic or serotonergic agents, lithium, anticonvulsants, or benzodiazepines).
* Psychiatric assessment that yields:1) history of severe suicide attempt, 2) current suicidality 3) first degree relative with schizophrenia or schizoaffective disorder, 4) comorbid substance use including cocaine, psychostimulant, or opioid use disorder within past 12 months and/or any use within past 30 days, 5) history of co-occurring psychotic episode/diagnosis including schizophrenia, schizoaffective disorder, schizophreniform, substance-induced psychosis, delusional disorder, or psychosis not otherwise specified, 6) high risk of adverse emotional or behavioral reaction based on the medical monitor's clinical evaluation that may also yield evidence of serious current stressors, a lack of meaningful social support, antisocial behavior, and/or serious personality disorders amongst other conditions.
* Medical assessment that yields: serious ECG abnormalities (evidence of ischemia, myocardial infarction, QTc prolongation \[QTc \> .045\]), serious abnormalities of complete blood count or chemistries, medical conditions that would preclude safe participation (significantly impaired liver function).
* MRI contraindication (pacemaker, etc.)
