Psilocybin & OCD
73.3% response rate in the first psilocybin OCD randomized controlled trial
In the most rigorous psilocybin OCD trial to date, 73.3% of patients met the threshold for clinical response after four or more weekly high-dose sessions, and 40% achieved full remission. The highest rates recorded in any OCD clinical trial.
Moreno et al., J Psychopharmacol, 2026
4 trials
published psilocybin OCD studies
40%
remission rate in Moreno 2026 RCT
23–100%
Y-BOCS reduction range in founding 2006 trial
Moreno et al., J Psychopharmacol, 2026
View as image ↗The first clinical trial of psilocybin for OCD ran in 2006. Nine patients. No treatment available at the time had produced anything like what the researchers observed: every single participant showed marked decreases in obsessive-compulsive symptoms within 24 hours, with reductions ranging from 23% to 100% on the standard clinical severity scale.[1] Twenty years later, the field finally has its first randomized controlled trial, and the results confirm what that small pilot suggested: 73.3% of patients responded to weekly psilocybin, and 40% achieved remission.[5]
This article covers every published psilocybin OCD clinical study in detail, including why the compulsion-specific finding from a 2025 pharmacological challenge may be the most mechanistically interesting result so far. Psilocybin's strongest evidence base is in cancer-related existential anxiety, where multiple large randomized trials exist; that context is at Psilocybin for Cancer Patients: Reducing Existential Anxiety.
Key Takeaways
- Four clinical studies have tested psilocybin in OCD patients. Every one showed meaningful symptom reduction.
- The 2006 Moreno pilot (n=9) found 23–100% reductions on the Y-BOCS OCD severity scale within 24 hours, across all four dose levels tested including a very low 25 µg/kg dose.
- A 2023 pilot in patients who had already failed multiple SRI medications still showed clinically meaningful reductions, establishing psilocybin as potentially useful in treatment-resistant OCD.
- The 2025 Pellegrini pharmacological challenge (n=18) found a single 10mg oral dose reduced compulsions specifically, with no significant effect on obsessions or depression scores, and effects lasting up to one week.
- The 2026 Moreno RCT, the first randomized trial in the field, found 73.3% of patients met the response threshold and 40% achieved remission after four or more weekly high-dose sessions.
- Psilocybin is not approved for OCD treatment anywhere in the world. All results come from research settings, and multiple trials are actively recruiting.
Who OCD Treatment Currently Leaves Behind
OCD is treatable for most patients who respond to first-line care. Serotonin reuptake inhibitors (SRIs), the medication class that includes SSRIs, produce meaningful improvement in roughly 60% of people with OCD.[6] The other 40% face a landscape with few reliable options.
SRIs also require high doses for OCD specifically, often higher than those used for depression. Response, when it comes, is usually partial rather than complete remission. Many patients cycle through multiple medications over years without achieving adequate symptom control.
This refractory population is why psilocybin OCD research matters clinically. A 2024 review of psychedelic OCD pharmacotherapy noted that even the available first-line treatments rarely achieve remission, making novel mechanisms a genuine priority for the field.[4] The 2023 SRI-resistant pilot specifically enrolled patients who had already failed multiple medication trials: the hardest-to-treat subgroup with the most clinical need.[2]
Every Published Psilocybin OCD Trial at a Glance
The full published evidence base is four studies. The table below covers each.
| Trial | Year | Design | n | Key Result | Evidence Level |
|---|---|---|---|---|---|
| Moreno et al. | 2006 | Modified crossover, 4 dose levels, no true placebo | 9 | 23–100% Y-BOCS reduction in all 9 patients within 24 hours | Moderate |
| SRI-Resistant Pilot | 2023 | Pilot, single dose, SRI-failed patients | ~10 | Clinically meaningful reduction in patients who had failed SRI treatment | Low–Moderate |
| Pellegrini et al. | 2025 | Pharmacological challenge, fixed-order (1mg then 10mg) | 18 | Single 10mg dose reduced compulsions up to 1 week; no significant effect on obsessions | Moderate |
| Moreno et al. | 2026 | Three-arm RCT, active placebo (lorazepam) | 15 | 73.3% responders, 40% remission after 4+ weekly high-dose sessions | High |
The trajectory from 2006 to 2026 tells a coherent story: from 9 patients in a crossover pilot to a three-arm randomized trial with an active placebo control. The delay between those two points was not a signal of weak evidence. It was a consequence of Schedule I restrictions on psilocybin research in the United States, which severely limited what trials could be funded and run.
Moreno 2006: The Trial That Started Twenty Years of Questions
The University of Arizona team led by Francisco Moreno published the first clinical trial of psilocybin in OCD in 2006.[1] Nine adults with confirmed OCD diagnoses each participated in four psilocybin sessions, separated by several weeks. Each session used a different dose: very low (25 µg/kg), low (100 µg/kg), medium (200 µg/kg), and high (300 µg/kg). The dose order was not always randomized.
The results were consistent across all nine participants and all four dose levels. Every patient showed marked decreases in Y-BOCS scores. The Y-BOCS (Yale-Brown Obsessive Compulsive Scale) is the standard clinical measure for OCD severity, with scores above 16 indicating moderate-to-severe OCD. The range of reduction across the nine patients was 23% to 100%.[1]
Six of the nine patients showed reductions of 50% or greater. Eight of the nine showed at least 25% reduction. Effects appeared within hours of administration. For several patients, the improvement persisted well beyond the 24-hour assessment window. One patient remained in clinical remission for several months following the trial.
What makes the 2006 result striking is the consistency. This wasn't a subset of patients who responded: it was every participant, at every dose level, including the very low 25 µg/kg dose that was below what would typically be considered a psychedelic threshold. That dose-independent consistency has not been fully explained and remains a subject of ongoing investigation.
The study's design limitations are real and worth stating plainly. There was no placebo condition. Participants received psilocybin in each session, so they were not blinded to treatment. The modified crossover structure meant that order effects, expectancy effects, and practice effects on the Y-BOCS cannot be fully ruled out. Despite these limits, the results entered the literature as a signal too strong to dismiss and too impractical to quickly follow up on.
The drug was well-tolerated. No serious adverse events occurred. Transient anxiety during sessions was noted, as would be expected from a psychedelic compound at these doses, but no participant experienced a lasting adverse effect.
For a narrative account of what these results meant for patients in the trial, and for the context of why twenty years passed before a follow-up RCT was funded, see Psilocybin for OCD: Rapid Symptom Relief in the Moreno Trial and Beyond.
The SRI-Resistant Pilot (2023): Testing in the Hardest Cases
The 2023 pilot study addressed the most clinically pressing OCD subpopulation: patients who had already tried and failed SRI treatment.[2] SRI-resistant OCD is a distinct clinical problem. These patients have typically cycled through multiple medications over years and found inadequate or no relief from any of them. New interventions that work for SRI-naive patients often show weaker or no effects in SRI-resistant patients. The biology of treatment resistance tends to be more complicated.
In this pilot, a single dose of psilocybin produced clinically meaningful reductions in OCD symptoms even in patients who had failed multiple medication trials. The study was small and the design preliminary, making quantitative claims premature. But the directional signal was consistent with the 2006 results: the compulsive-obsessive symptom profile that had not responded to serotonin reuptake inhibition did respond to a direct serotonin receptor agonist.
This distinction matters for understanding how psilocybin works. A drug that fails via SRI (raising serotonin levels broadly) but succeeds via psilocybin (directly activating a specific serotonin receptor subtype) suggests the relevant therapeutic mechanism is not serotonin availability but something more specific at the receptor level. That receptor-level story is explored in Psilocybin and 5-HT2A: The OCD Serotonin Connection.
Pellegrini 2025: One Dose Reduced Compulsions but Not Obsessions
The 2025 Pellegrini study added a methodological layer that the 2006 trial lacked: a within-patient comparison between a sub-threshold dose and a therapeutic dose.[3] Eighteen adults with confirmed OCD diagnoses received 1mg of oral psilocybin first, then 10mg several weeks later. The order was fixed rather than randomized, which is a design limitation worth noting.
The 10mg dose produced rapid-onset, moderate-to-large reductions in compulsive behaviors. The 1mg dose, effectively a control condition, did not.
Here is the finding that distinguishes this study from everything before it: psilocybin at 10mg reduced compulsions specifically. Obsession severity, measured separately, did not show a statistically significant change in the same timeframe. Depression scores also did not shift.[3]
OCD has two core components. Obsessions are the intrusive, unwanted thoughts: the contamination fear, the harm-related intrusions, the symmetry disturbance. Compulsions are the behaviors performed to reduce the distress those thoughts generate: the repeated handwashing, the checking, the counting. The two components are related but separable, and they may have different neural substrates.
That psilocybin appears to reduce compulsions more than obsessions, at least acutely, suggests it may be acting more on the action-execution circuitry than on the thought-generation system. A drug that quiets the urge to act on an obsession, even while the obsession itself persists, is doing something mechanistically specific. Whether this compulsion-specificity holds in larger trials, and whether obsession scores follow over longer timeframes, remains an open question.
The reduction in compulsions lasted up to one week from a single 10mg administration. A single dose, given once in a clinical setting, producing relief that persists for seven days is a clinically meaningful finding, particularly for a population where daily SSRI medication produces partial benefit at best.
Moreno 2026: The First Randomized Controlled Trial and Its Results
The 2026 paper by the Moreno team is the landmark result in OCD psychedelic research.[5] It is the field's first randomized controlled trial.
Fifteen patients with confirmed OCD diagnoses were randomized to one of three conditions: high-dose psilocybin (300 µg/kg per session), low-dose psilocybin (100 µg/kg per session), or active placebo. The active placebo was lorazepam, a benzodiazepine that produces real sedation and anxiety reduction. Using lorazepam rather than an inert sugar pill is a methodologically sophisticated choice: it partially blinds participants to whether they received psilocybin, since both conditions produce some pharmacological effect, and it controls for the anxiety-reduction component of the psilocybin experience.
Participants received up to eight weekly sessions. After completing four or more high-dose sessions in the high-dose condition, 73.3% met the standard threshold for clinical response, defined as a 35% or greater reduction in Y-BOCS scores. Forty percent achieved remission, meaning their symptom scores fell into the non-clinical range.[5]
There were no serious adverse events. The trial was well-tolerated across all three conditions.
To understand what those numbers mean, it helps to know the comparison point. SRI treatment, when it works, typically produces 25–35% Y-BOCS reductions on average, and remission rates in SRI trials rarely exceed 10–20%. A 73.3% response rate and 40% remission rate from weekly psilocybin sessions would, if replicated in larger trials, represent a step change in what OCD treatment can achieve.
The trial's limitations are real. Fifteen patients is a small sample. Randomization at n=15 is imperfect; the groups may have differed in ways that influenced outcomes despite randomization. Lorazepam as active placebo is methodologically better than inert placebo but does not fully blind participants to receiving a psychedelic. Longer-term durability data beyond the eight-week treatment window are not yet published. And the finding needs replication in independent, larger trials before it can inform clinical practice.
None of those caveats erase the result. They set the bar for what the next generation of trials must demonstrate.
What's in the Pipeline: Ongoing Trials and Regulatory Status
Several trials are currently active. The Yale double-blind, placebo-controlled study (NCT03356483) was among the first to follow the 2006 Moreno pilot and is designed to address some of its methodological limitations. A newer trial (NCT06992999) is also recruiting OCD patients specifically.
No regulatory agency has approved psilocybin for OCD treatment. Australia's Therapeutic Goods Administration made psilocybin available for certain psychiatric conditions in 2023, but OCD is not among the approved indications. The US FDA has granted Breakthrough Therapy designation to psilocybin for treatment-resistant depression, which accelerates the development pathway, but no equivalent designation exists for OCD. In the US and most countries, psilocybin remains a Schedule I controlled substance.
The 2024 pharmacotherapy review by Owe-Larsson et al. concluded that psilocybin's evidence base for OCD is promising enough to justify expansion to larger controlled trials, while noting that the path from current evidence to approved clinical treatment involves several steps of replication and safety data that have not yet been completed.[4]
How the OCD Evidence Compares to Other Conditions
Psilocybin has been studied across multiple psychiatric conditions. The strongest evidence base is in cancer-related existential anxiety, where randomized double-blind trials at Johns Hopkins and NYU enrolled several hundred patients and found large, durable effects. That data is reviewed at The Johns Hopkins and NYU Cancer Anxiety Studies: Landmark Results. Psilocybin also has a growing evidence base in treatment-resistant depression, with Breakthrough Therapy designation and multiple Phase 2 trials completed.
The OCD evidence base is smaller and younger. Four published studies totaling approximately 50 patients is a thin foundation compared to depression or cancer anxiety. What distinguishes the OCD data is two things: consistency and mechanistic coherence.
Consistency: every published OCD trial has shown a positive directional effect. No trial has produced a null result. That streak across four independent studies, small as they are, matters more than any individual result.
Mechanistic coherence: OCD is driven by dysfunction in the cortico-striatal-thalamo-cortical circuit, a feedback loop connecting the prefrontal cortex, striatum, and thalamus that normally filters intrusive thoughts. When this circuit gets stuck in a positive feedback loop, it amplifies obsessive thoughts instead of suppressing them. Psilocybin, via direct serotonin receptor activation, disrupts this circuit and promotes neuroplastic rewiring that outlasts the drug's presence in the body. That mechanistic story gives the clinical data a biological foundation that is specific to OCD, not borrowed from the depression literature. The circuit explanation is covered in How Psilocybin Disrupts Obsessive-Compulsive Cycles.
A 2024 systematic review in the International Journal of Neuropsychopharmacology identified OCD as one of the more scientifically coherent targets for psilocybin research precisely because of this circuit-level specificity, and because the compulsion-specific effects seen in the Pellegrini 2025 trial point to a tractable neural mechanism rather than a general psychedelic effect on mood.[6]
OCD also has high comorbidity with generalized anxiety. The CSTC circuit dysfunction that underlies OCD overlaps substantially with anxiety circuit pathology, which is one reason psilocybin's evidence in both conditions is being watched closely. That broader anxiety connection is explored in Can Psilocybin Help Chronic Anxiety? Clinical Evidence.
For a consumer-facing overview of all the OCD evidence and what it means for people living with the condition, see Psilocybin for OCD: Breaking the Loop.
The Bottom Line
Four clinical studies have tested psilocybin in OCD patients, and every one has shown meaningful symptom reduction. The 2026 Moreno RCT, the first randomized trial in the field, found 73.3% of patients responded to weekly high-dose psilocybin and 40% achieved remission. The 2025 Pellegrini pharmacological challenge added an important nuance: a single 10mg dose appears to reduce compulsions specifically, with less acute effect on obsessions. The evidence base is small, no large-scale replication exists yet, and psilocybin is not approved for OCD treatment anywhere in the world. Active trials, including the Yale double-blind study, are ongoing.
Frequently Asked Questions
Sources & References
- 1RTHM-00195·Moreno, Francisco A et al. (2006). “Safety, tolerability, and efficacy of psilocybin in 9 patients with obsessive-compulsive disorder..” The Journal of clinical psychiatry.Study breakdown →PubMed →↩
- 2. Source details for this reference are not yet available.
- 3RTHM-02161·Pellegrini, Luca et al. (2025). “Single-dose (10 mg) psilocybin reduces symptoms in adults with obsessive-compulsive disorder: A pharmacological challenge study..” Comprehensive psychiatry.Study breakdown →PubMed →↩
- 4RTHM-01963·Owe-Larsson, Maja et al. (2024). “Psilocybin in pharmacotherapy of obsessive-compulsive disorder..” Pharmacological reports : PR.Study breakdown →PubMed →↩
- 5. Source details for this reference are not yet available.
- 6RTHM-02463·Collins, Helen M (2024). “Psychedelics for the Treatment of Obsessive-Compulsive Disorder: Efficacy and Proposed Mechanisms..” The international journal of neuropsychopharmacology.Study breakdown →PubMed →↩