Safety, Tolerability, and Efficacy of Psilocybin in 9 Patients With Obsessive-Compulsive Disorder

This double-blind study (n=9) of psilocybin (up to 21mg/70kg) found no adverse effects and improvements in OCD symptoms. Immediate improvements on the Yale-Brown Obsessive Compulsive Scale (YBOCS) varied between 23-100% reductions. Positive effects were also observed after the 24 hours reported in the study.


“Anecdotal reports suggest that psychedelic agents may relieve symptoms of obsessive-compulsive disorder (OCD). This modified double-blind study investigated the safety, tolerability, and clinical effects of psilocybin, a potent 5-HT(1A) and 5-HT(2A/2C) agonist, in patients with OCD. Nine subjects with DSM-IV-defined OCD and no other current major psychiatric disorder participated in up to 4 single-dose exposures to psilocybin in doses ranging from sub-hallucinogenic to frankly hallucinogenic. Low (100 microg/kg), medium (200 microg/kg), and high (300 microg/kg) doses were assigned in that order, and a very low dose (25 microg/kg) was inserted randomly and in a double-blind fashion at any time after the first dose. Testing days were separated by at least 1 week. Each session was conducted over an 8-hour period in a controlled environment in an outpatient clinic; subjects were then transferred to a psychiatric inpatient unit for overnight observation. The Yale-Brown Obsessive Compulsive Scale (YBOCS) and a visual analog scale measuring overall obsessive-compulsive symptom severity were administered at 0, 4, 8, and 24 hours post-ingestion. The Hallucinogen Rating Scale was administered at 8 hours, and vital signs were recorded at 0, 1, 4, 8, and 24 hours after ingestion. The study was conducted from November 2001 to November 2004. Nine subjects were administered a total of 29 psilocybin doses. One subject experienced transient hypertension without relation to anxiety or somatic symptoms, but no other significant adverse effects were observed. Marked decreases in OCD symptoms of variable degrees were observed in all subjects during 1 or more of the testing sessions (23%-100% decrease in YBOCS score). Repeated-measures analysis of variance for all YBOCS values revealed a significant main effect of time on Wilks lambda (F = 9.86, df = 3,3; p = .046), but no significant effect of dose (F = 2.25, df = 3,3; p = .261) or interaction of time and dose (F = 0.923, df = 9,45; p = .515). Improvement generally lasted past the 24-hour timepoint. In a controlled clinical environment, psilocybin was safely used in subjects with OCD and was associated with acute reductions in core OCD symptoms in several subjects.”

Authors: Francisco A. Moreno, Christopher B. Wiegand, E. Keolani Taitano & Pedro L. Delgado


This paper is reviewed by Edwards (2020).

Summary of Safety, Tolerability, and Efficacy of Psilocybin in 9 Patients With Obsessive-Compulsive Disorder

OCD is the fourth most common psychiatric diagnosis and has a high disease burden. Many patients with OCD delay or altogether avoid pursuing care.

SRIs are among the most effective pharmacologic treatments for OCD, although they reduce symptoms by only 30% to 50%. Some SRI-treated patients who receive the 5-HT2 antagonist metergoline experience a resurgence of OCD symptoms.

OCD is a chronic and debilitating condition with a lifetime prevalence. Although treatment with SRIs is quite extensive, the rates of remission are minimal, and many patients considered responders have residual symptoms.

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Safety, Tolerability, and Efficacy of Psilocybin in 9 Patients With Obsessive-Compulsive Disorder

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Published in
Journal of Clinical Psychiatry
October 1, 2006
663 citations

Study details

Compounds studied

Topics studied
Obsessive-Compulsive Disorder

Study characteristics
Original Placebo-Controlled Active Placebo Double-Blind Within-Subject

9 Humans


Authors associated with this publication with profiles on Blossom

Francisco Moreno
Francisco A. Moreno, M.D. is Professor of Psychiatry and Associate Vice President at the University of Arizona


Institutes associated with this publication

University of Arizona
Dr Franscio Moreno at the University of Arizona has been exploring the potential of psychedelic's to treat OCD.

Compound Details

The psychedelics given at which dose and how many times

Psilocybin 7 - 21
mg | 4x

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