A new systematic review led by University of Melbourne researchers finds psilocybin reduces obsessive and compulsive symptoms across multiple small human studies and robust animal models, while underscoring the need for larger, placebo-controlled trials to determine true efficacy and dosing.
The review screened 396 papers and included 13 studies: 4 clinical and 9 preclinical.
In humans, one small early study in hard-to-treat OCD found symptoms dropped noticeably within 4–24 hours after psilocybin. Another small study in body dysmorphic disorder gave a single 25 mg dose and saw steady improvement over 12 weeks, with about 58% showing a strong response by week 12.
A newer OCD study that used 1 mg first and 10 mg at least four weeks later saw the biggest improvement one week after the 10 mg dose—mainly in repetitive behaviors—but the benefit faded by four weeks.
An online survey also tied psilocybin mushrooms to fewer obsessions and compulsions, with about one-third saying the benefits lasted more than three months.
Overall, the results are encouraging, but the studies were small, didn’t always include a control group, and used different methods, so stronger trials are still needed.
Animal studies were more consistent. In SAPAP3 knockout mice, a leading model of compulsive grooming, single psilocybin doses reduced pathological grooming with effects lasting from one to seven weeks. Standard marble-burying results were mixed, echoing debates about that assay’s validity for compulsivity. Mechanistically, several experiments suggest psilocybin’s anti-compulsive actions can occur independently of 5-HT2A activation, raising the possibility that non-hallucinogenic dosing or analogs could retain benefit. Signals of synaptic and circuit-level plasticity further support durable changes underlying behavioral improvements.
The authors call for randomized, adequately powered trials in OCD and the broader obsessive-compulsive and related disorders spectrum, with active placebos, head-to-head dosing strategies (single high dose vs. repeated low dose), neuroimaging of cortico-striatal circuits, and planned analyses by sex. Early cross-species convergence—rapid, meaningful reductions in compulsive behavior followed by partial decay—suggests a real therapeutic signal that now needs rigorous confirmation.
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