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Efficacy of high- and low-dose psilocybin in preventing relapse in adults with severe alcohol use disorder and depressive symptoms after detoxification

Verified siteInvestigationalNo placebo
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What is this trial about?

A plain-language summary of the goals, design and what participants do

The study focuses on individuals with Alcohol use disorder who also experience depressive symptoms. The investigational medication is psilocybin, a compound taken in capsule form by mouth.

The aim is to compare the effect of two larger doses given three weeks apart with two smaller doses given on the same schedule, to see which approach better prevents a return to heavy drinking after a period of detoxification. Participants will receive the assigned capsules, attend regular check‑in visits, and record their drinking using a calendar method that helps recall daily alcohol use.

During the six‑month follow‑up, researchers will note the first day a participant drinks a large amount (defined as at least 60 g of alcohol) and will collect information on mood, anxiety, and overall quality of life at several points. Blood samples will also be taken at the start and near the end of the study to monitor safety.

The research process

The trial runs in 10 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Baseline assessment

    At the first visit, complete a set of questionnaires that ask about drinking habits, mood, anxiety, and daily functioning; these are explained as simple surveys about alcohol use and emotional well‑being.

    Provide a blood sample for laboratory analysis; this is a routine collection of a small amount of blood.

    The study staff record the amount of alcohol consumed in the previous weeks using the timeline follow-back method, which involves marking a calendar with drinking days.

  2. Step 2

    First dose administration

    Receive a single capsule for oral use containing either 25 mg of psilocybin (the high dose) or 3 mg of psilocybin (the low dose), depending on the assigned group.

    Take the capsule by swallowing it with water under supervision at the clinic.

  3. Step 3

    Post‑dose observation and integration session

    Remain at the clinic for a short observation period to ensure safety after the dose.

    Attend an integration session in which a therapist helps understand the experience; this session is optional but recommended for all participants.

  4. Step 4

    Second dose administration

    Three weeks after the first dose (week 3), receive a second identical capsule of the assigned dose (25 mg or 3 mg) and swallow it with water.

    Stay for the same brief observation period as after the first dose.

  5. Step 5

    Follow‑up visits – weeks 9, 15, and 21

    Attend clinic visits at weeks 9, 15, and 21 to complete the same set of questionnaires used at baseline.

    Provide additional blood samples as requested.

    Record alcohol consumption for the preceding weeks using the timeline follow-back calendar.

  6. Step 6

    Week 27 assessment and possible third dose

    Undergo a comprehensive assessment that includes questionnaires, blood sampling, and a review of drinking patterns.

    If eligible and willing, receive a third capsule containing 25 mg of psilocybin (the third dose) administered at the clinic.

    The decision to receive the third dose is based on the participant’s relapse status and personal preference.

  7. Step 7

    Post‑third‑dose follow‑up – weeks 33, 39, 45, and 51

    Attend visits at weeks 33, 39, 45, and 51 to repeat questionnaires, provide blood samples, and update the timeline follow-back record of alcohol use.

    These visits monitor any changes after the third dose and continue safety assessments.

  8. Step 8

    Week 28 assessment

    Complete a brief set of questionnaires that focus on recent experiences and any adverse effects; no medication is taken at this visit.

  9. Step 9

    Primary outcome evaluation – 6‑month follow‑up

    At approximately six months after the first dose, the study determines whether a heavy drinking day (defined as consuming 60 g or more of alcohol) has occurred.

    The time until the first heavy drinking day is recorded as the primary measure of relapse.

  10. Step 10

    12‑month follow‑up for high‑dose group

    Participants who received the high dose complete a final set of questionnaires and provide a blood sample between 6 and 12 months after the first dose.

    These data compare outcomes between those who received a third dose and those who did not.

Who can join the trial?

6 criteria

  • Have a confirmed diagnosis of severe alcohol use disorder (AUD) according to the DSM‑5 guidelines, which is a standard manual doctors use to define mental health conditions.
  • Score of 14 or higher on the Beck Depression Inventory (BDI‑II), a questionnaire that measures how strong depressive symptoms are.
  • Had your last drink of alcohol between 10 and 60 days before the screening visit, and during the four weeks before that last drink you had at least one heavy drinking day (HDD) (a day when a large amount of alcohol was consumed).
  • Be able to give informed and voluntary consent, meaning you understand the study and agree to take part without pressure.
  • Be covered by a health insurance plan or be a beneficiary of one.
  • Be an adult (18 years old or older).

Who cannot join the trial?

32 criteria

  • Used any classical psychedelic (such as LSD or psilocybin) in the past year.
  • Scored higher than 8 on the CIWA‑AR test, which measures alcohol‑withdrawal symptoms.
  • Have a seizure disorder (a condition that causes seizures or fits).
  • Have serious liver problems (the liver does not work well).
  • Have coronary artery disease (blocked arteries in the heart).
  • Have a history of arrhythmia (irregular heartbeat).
  • Have a prolonged QT interval (a heart rhythm problem measured by an ECG; QTc > 470 ms for women or > 450 ms for men).
  • Have heart failure (the heart cannot pump blood effectively).
  • Have uncontrolled high blood pressure (greater than 165 / 95 mmHg at screening).
  • Have had a stroke.
  • Have severe asthma (serious lung disease that makes breathing difficult).
  • Have hyperthyroidism (an overactive thyroid gland).
  • Have narrow‑angle glaucoma (an eye disease that can increase eye pressure).
  • Have a severe stomach ulcer that blocks the stomach or duodenum (gastroduodenal ulcer or pyloroduodenal obstruction).
  • Have urinary blockage from an enlarged prostate (symptomatic prostatic hypertrophy) or bladder neck obstruction.
  • Have uncontrolled type I or type II diabetes, or a history of diabetic ketoacidosis, hyperglycemic coma, or severe low blood sugar that caused loss of consciousness.
  • Are currently taking part in another clinical trial or interventional study.
  • Are in a required waiting period after another study.
  • Are under legal protection, guardianship, or curatorship (someone else makes legal decisions for you).
  • Cannot give informed consent (cannot understand and agree to the study).
  • Cannot be given enough information to understand the study.
  • Plan to donate sperm within three months of receiving psilocybin.
  • Have a positive pregnancy test (if you could become pregnant).
  • Are pregnant, breastfeeding, or plan to become pregnant during the study.
  • Have another current substance use disorder (except tobacco).
  • Have been diagnosed with schizophrenia or bipolar disorder (serious mental health conditions).
  • Have high emotional lability (very rapid mood changes judged by a clinician).
  • Are taking antipsychotic medications that could interfere with psilocybin.
  • Need treatment with a monoamine oxidase inhibitor (MAOI) that could interfere with psilocybin.
  • Have severe suicidal thoughts (high risk on the Columbia scale, a suicide‑risk questionnaire).
  • Have a first‑degree family member (parent, sibling, or child) with a diagnosed psychotic disorder.
  • Have severe cognitive impairment (significant problems with thinking and understanding, judged by a clinician).
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Investigated drugs

  • Psilocybin (high dose)

    is a naturally occurring compound that produces psychedelic effects when taken by mouth in capsule form. In this study, participants receive two sessions of the medication, spaced three weeks apart, after completing alcohol detoxification. The purpose of the high‑dose psilocybin is to see if it can help reduce the chance of returning to heavy drinking in people who also have depression.

  • Psilocybin (low dose)

    is the same psychedelic compound, but given in a much smaller amount. Like the high‑dose version, it is taken as a capsule orally and is administered twice, three weeks apart. The low‑dose regimen serves as a comparison to determine whether a smaller amount of psilocybin provides any benefit in preventing relapse to excessive alcohol use.

What is already known about the treatment

  • Psilocybin

    Psilocybin is taken as an oral capsule that is swallowed with water. It is a psychedelic compound that is still under research and is not yet approved as a regular medicine. In this trial it is being tested for helping people with alcohol use disorder who also have depressive symptoms. It works by briefly activating serotonin receptors in the brain, especially the 5‑HT2A type, and is classified as a serotonergic psychedelic.

  • Psilocybin

    This form of psilocybin is also given as an oral capsule that is swallowed with water. It is a low‑dose version of a psychedelic that is still being studied and has no approved medical use at present. The trial uses it as a comparison to see if a smaller amount can affect alcohol use disorder with depression. Like the higher dose, it briefly activates serotonin receptors in the brain and belongs to the serotonergic psychedelic class.

Investigated diseases

  • Alcohol use disorder

    A chronic condition where a person cannot control how much they drink, leading to steadily increasing consumption. It often starts with occasional heavy drinking and can develop into regular, larger amounts that cause physical dependence. Over time, cravings become stronger and attempts to cut back become difficult. The body builds tolerance, so more alcohol is needed to feel the same effect. The pattern may include cycles of heavy drinking followed by attempts to stop.

  • Depressive disorder

    A mood condition marked by ongoing sadness, loss of interest, and low energy. It typically begins with a mild low mood that worsens over weeks, affecting everyday activities. As it progresses, thoughts become more negative, sleep and appetite may change, and concentration can decline. The severity can increase, leading to feelings of hopelessness. Without change, the symptoms tend to remain present and may fluctuate.

Trial detailsLast updated 7 Oct 2026
Age18+ yearsPhasePhase IIITrial ID2025-525069-65-00Estimated enrolment172 patientsSponsorCentre Hospitalier Universitaire De Nimes

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