Psilocybin Shows Promise in Treating OCD and Tourette’s Syndrome

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Psilocybin for OCD and Tourette Syndrome

Psilocybin is being studied as an experimental treatment for obsessive-compulsive disorder (OCD). Small human studies published through 2026 have reported reductions in OCD symptoms after supervised psilocybin administration, though the evidence remains too limited to establish effectiveness, an accepted dose or long-term safety. Evidence for Tourette syndrome is much earlier. The study often cited in connection with both conditions involved genetically modified mice and did not test psilocybin in people with Tourette syndrome. Psilocybin has no approved role in treating OCD or Tourette syndrome in the United States. 1 2 3

What OCD and Tourette Syndrome Involve

OCD is a psychiatric disorder involving obsessions, compulsions or both. Obsessions are recurring, intrusive and unwanted thoughts, urges or mental images. Compulsions are repetitive behaviors or mental acts that a person feels driven to perform. A diagnosis requires clinical assessment because intrusive thoughts, repetitive behavior, anxiety and rigid routines can occur in several psychiatric, neurologic and developmental conditions. 4

The National Institute of Mental Health (NIMH) estimates that 1.2 percent of US adults had OCD during the previous year and 2.3 percent experienced it during their lifetime. These figures come from interviews conducted in 2001 through 2003 using diagnostic criteria in effect at that time. Among adults identified as having OCD in the previous year, 50.6 percent were classified as having serious impairment. 5

Tourette syndrome is a neurodevelopmental disorder involving motor tics and vocal tics. Tics are sudden, repeated movements or sounds. Diagnostic criteria require at least two motor tics and one vocal tic at some point, symptoms lasting at least one year and onset before age 18. The symptoms also must not be caused by a medicine, another drug or another medical condition. There is no single blood test or brain scan that confirms the diagnosis. A clinician assesses the type of movements or sounds, age at onset, duration and possible alternative causes. 6

OCD and Tourette syndrome can occur in the same person. The Centers for Disease Control and Prevention (CDC) advises clinicians to assess people with Tourette syndrome for coexisting conditions such as OCD, attention-deficit/hyperactivity disorder and anxiety. Each condition still requires its own assessment and treatment plan. 7

What the Psilocybin Mouse Study Actually Tested

The 2024 study that generated many reports about psilocybin, OCD and Tourette syndrome was a randomized experiment in 50 SAPAP3 knockout mice. These mice develop excessive self-grooming, anxiety-related behavior and head-body twitches. Researchers use this model to study selected features that may have relevance to compulsive behavior. A mouse model cannot reproduce human obsessions, the personal distress associated with OCD or the diagnostic features of Tourette syndrome. 2

The mice received one injection of synthetic psilocybin, a mushroom extract containing an equivalent psilocybin dose or a vehicle control. A rater who did not know each animal’s treatment assessed behavior after 2, 12 and 21 days. Total self-grooming increased in the vehicle group and decreased in both psilocybin groups during the observation period. Head-body twitches and anxiety-related measures also changed in the treated groups. 2

Several details limit the direct clinical meaning of these results. Five mice in the vehicle group and four in the synthetic psilocybin group were removed after developing skin lesions. The longest follow-up analysis included treatment responders, which can make an effect appear larger or more durable. The dose was delivered by injection and the mushroom extract contained compounds other than psilocybin. Human psilocybin studies usually use a standardized oral product under medical supervision. 2

The mouse head-body twitches were treated as a behavior with possible relevance to tics. They do not show that psilocybin reduces motor or vocal tics in people. The study supports further laboratory and clinical research. It provides no basis for describing psilocybin as an effective Tourette treatment.

What Human Studies Show About Psilocybin for OCD

Human research has moved past isolated case reports, though the published studies remain small. Differences in dose, study design, control conditions and follow-up make firm comparisons difficult.

The 2006 Pilot Study

A 2006 pilot study administered 29 psilocybin doses to nine adults with OCD. Each participant received several dose levels under supervision. Researchers observed acute reductions in Yale-Brown Obsessive Compulsive Scale scores during one or more sessions, though improvement did not follow a clear dose-response pattern. The study was small and lacked a conventional placebo control group, so expectancy, repeated assessments and natural symptom variation could have influenced the results. 8

The 2025 Pharmacological Challenge Study

A 2025 study enrolled 19 adults with at least moderate OCD and obtained complete follow-up from 18. Every participant received 1 mg of oral psilocybin followed four weeks later by 10 mg. The fixed order means participants were not randomly assigned to dose sequence. Psychological support and clinical monitoring were provided before, during and after administration. 9

One week after the 10 mg dose, OCD scores were lower than after the 1 mg dose, with the clearer difference found on the compulsion subscale. The effect decreased during the next three weeks. The study reported few adverse events and no serious adverse event. Its small sample, fixed treatment order, mild psychoactive effects and lack of a separate placebo group limit the certainty of the efficacy finding. 9

The 2026 Repeated-Dose Trial

A 2026 phase 1 study randomized 15 adults with moderate to severe OCD to four weekly sessions of higher-dose psilocybin, lower-dose psilocybin or lorazepam as an active placebo. Each group contained five participants. The initial randomized phase was followed by four weekly higher-dose psilocybin sessions for the participants. The trial used screening, preparation, prolonged supervised sessions and frequent psychiatric assessments. 1

The investigators reported lower OCD scores with psilocybin and no serious adverse events, psychotic symptoms or significant change in suicide severity scores. At the end of eight weeks, 73.3 percent of the 15 participants met the study definition of response and 40 percent met its definition of remission. By that point, all participants included in the treatment sequence had received at least four higher-dose sessions. Those percentages therefore do not represent a controlled comparison with placebo. 1

The randomized phase had only five people in each group and was not powered to provide a reliable between-group efficacy test. One participant withdrew after anxiety and an intense emotional reaction during a placebo session. Another left after a lower-dose session because of discomfort with the lengthy session procedure. The results support larger controlled trials and do not establish psilocybin as standard OCD treatment. 1

What Human Evidence Shows for Tourette Syndrome

The published mouse study did not enroll people with Tourette syndrome and did not measure human motor or vocal tics. No completed human trial reviewed for this article has shown that psilocybin reduces tic severity, tic-related impairment or coexisting OCD symptoms in people with Tourette syndrome.

This distinction is medically important. A head-body twitch in a mouse is an experimental behavior. Tourette syndrome is a human neurodevelopmental diagnosis with varied motor and vocal tics, changing symptom patterns and frequent coexisting conditions. A treatment that changes one behavior in a mouse may have different effects in a person. 2 10

Current Tourette guidance includes education, watchful waiting when tics are not impairing, the behavioral program known as CBIT and selected medicines when symptoms cause pain, injury, distress or interference with daily activities. Psilocybin is not included as a recommended treatment. 11 12

How Psilocybin May Affect Brain Function

Psilocybin is converted in the body to psilocin. Psilocin acts at several serotonin receptors and its psychoactive effects are strongly linked to serotonin 2A receptor activity. Researchers have proposed that changes in serotonin signaling, brain network activity, cognitive flexibility and learning could have relevance to OCD. The pathway connecting these changes to lasting symptom improvement has not been established. 1

Descriptions such as resetting the brain or breaking a compulsive circuit go further than the evidence. Human OCD studies have mainly measured symptoms and tolerability in small, highly screened groups. They have not shown that a specific brain change causes clinical improvement. The psychological support, expectations, study setting and repeated contact with clinicians may also affect reported outcomes.

How Current Treatments Compare

Established OCD Care

Evidence-based OCD treatment commonly includes cognitive behavioral therapy with exposure and response prevention (ERP), medication or both. ERP uses planned exposure to an obsession trigger while helping you refrain from the usual compulsion. Selective serotonin reuptake inhibitors are commonly prescribed and may require 8 to 12 weeks before improvement becomes clear. Treatment choice depends on age, symptom severity, other diagnoses, prior treatment, pregnancy status, current medicines and access to trained clinicians. 4

Some people continue to have substantial symptoms after adequate treatment. A clinician may review the diagnosis, therapy quality, medication duration, dose, adherence and coexisting conditions before considering another intervention. Brain stimulation is available for selected people with severe OCD under specific regulatory and clinical conditions. 4

The current psilocybin studies do not show that psilocybin works better than ERP, an established medication plan or combined treatment. They also do not show that one or several psilocybin sessions can replace daily medication. Direct comparative trials would be needed to support those claims.

Established Tourette Care

Many people with Tourette syndrome do not need tic treatment when symptoms cause little impairment. CBIT can reduce tic frequency, severity or tic-related impairment for some children and adults. Medicines may be considered when tics cause pain, injury, distress or problems at school, work or in social life. Medication benefits and adverse effects vary, so treatment should focus on the symptoms causing the greatest impairment. 11 12

Coexisting OCD, attention-deficit/hyperactivity disorder, anxiety or depression may require separate care. Improvement in one condition does not guarantee improvement in another.

Psilocybin Safety and Research Screening

Controlled psilocybin studies use medical and psychiatric screening, standardized study material, supervised administration and follow-up. Common acute adverse effects reported across randomized depression and anxiety trials include headache, nausea, anxiety, dizziness and temporary blood pressure changes. Most reported acute effects resolved within 24 to 48 hours. Rare events and long-term risks remain less certain because study samples have been modest and participants with several medical or psychiatric risks were often excluded. 13

OCD trials have commonly excluded people with psychotic disorders, mania, uncontrolled hypertension, serious cardiac disease, active substance use disorders, recent suicide attempts, pregnancy or breastfeeding. Medication restrictions have also been used. These criteria limit the findings to screened participants and should not be treated as a safety finding for people who were excluded. 1

Do not stop an antidepressant, antipsychotic, mood stabilizer or other prescribed medicine to seek psilocybin treatment or trial entry without guidance from your prescriber and the study physician. Withdrawal, relapse and drug interactions can create significant risk. 4

Psilocybin-containing mushrooms are not equivalent to the standardized products used in clinical studies. Dose, concentration and composition can vary. Products may contain contaminants. Findings from supervised research cannot be applied directly to self-directed use. 14

What Researchers Still Need to Establish

Larger randomized trials need to answer several questions before psilocybin could have an accepted role in OCD care.

The size of benefit compared with a credible placebo and established treatment
The number of sessions and dose range needed for a sustained response
The durability of improvement after treatment ends
The effect on obsessions, compulsions, functioning and daily life
The contribution of psychological preparation and follow-up support
Safety in people with common psychiatric and medical conditions
Interactions with serotonin reuptake inhibitors and other medicines
Risks linked to repeated dosing

Tourette research requires an earlier step. Researchers would need controlled human trials that directly measure motor tics, vocal tics, impairment and adverse events. The mouse findings alone cannot predict those outcomes.

What This Means for You

You should continue established care if you have OCD, Tourette syndrome or both. Psilocybin remains an experimental intervention and should not replace ERP, CBIT, prescribed medication or clinical follow-up.

If you are considering a clinical trial, read the official registry entry and discuss it with the study team and your own clinician. Ask about the control group, dose schedule, medication restrictions, screening criteria, supervision, adverse-event plan and follow-up period. Trial participation may involve risks and may provide no personal benefit.

Seek a clinical assessment if intrusive thoughts, rituals, movements or sounds are causing distress or interfering with daily life. Sudden or unusual movements can have several causes, including medication effects, seizures, functional neurologic symptoms and other movement disorders. A qualified clinician should assess new or unexplained symptoms. 6

If you are in the United States and experiencing suicidal thoughts or a mental health crisis, call or text 988. Call 911 in an immediate life-threatening situation. 4