Dr Sorcha O'Connor: The PsilOCD Study Investigating Low-Dose Psilocybin for OCD (#532)

The PsilOCD study, led by Dr. Saoirse O'Connor at Imperial College London, was Europe’s first controlled trial of low‑dose psilocybin for obsessive‑compulsive disorder. Nineteen adults aged 20‑60 were screened for psychiatric safety, received a week of preparatory therapy, a micro‑dose placebo, four weeks of follow‑up, then a 10 mg psilocybin dose followed by another four‑week therapeutic period. Eighteen participants completed the protocol, providing a diverse sample of OCD symptom dimensions, from contamination to responsibility concerns. This design allowed researchers to isolate the pharmacological effect while maintaining a supportive therapeutic context.

Results showed a rapid, clinically meaningful reduction in Yale‑Brown Obsessive‑Compulsive Scale (Y‑BOCS) scores. Approximately 39‑40% of participants achieved a strong response—defined as >35% improvement—within one week of the 10 mg dose, and ten individuals moved from moderate‑severe to mild symptom categories. The benefit persisted at the two‑week mark for completers but declined to non‑significance by four weeks, suggesting a transient window of heightened neuro‑cognitive openness. Contrary to expectations, EEG‑based assays did not reveal increased neuroplasticity, highlighting the need for more sensitive biomarkers and for integrating exposure and response prevention (ERP) or ACT during the post‑dose window.

The study’s implications extend beyond OCD. Low‑dose psilocybin may fit within precision psychiatry frameworks, offering a short‑acting adjunct to established psychotherapies rather than a standalone medication. Ongoing U.S. trials are testing higher doses (25‑30 mg) to compare efficacy and durability, while companies like Compass Pathways push toward FDA approval for treatment‑resistant depression, potentially paving the way for broader psychedelic indications. Future research should combine controlled dosing with structured ERP, explore optimal spacing of multiple doses, and clarify long‑term safety, positioning psilocybin as a promising, albeit still experimental, tool in the mental‑health arsenal.