This study aims to investigate the effects of repeated dosing of oral psilocybin on obsessive-compulsive disorder (OCD) symptomatology in a randomized, waitlist-controlled design with blinded independent ratings, and assess psychological mechanisms that may mediate psilocybin's therapeutic effects on OCD.
Randomized, waitlist-controlled, single-blind (independent rater) parallel design (n=30) comparing immediate two-dose oral psilocybin (25 mg first dose; second dose 25 or 30 mg based on response after 4 days) versus a 7-week delayed treatment.
Outpatient treatment with two preparatory sessions and two integration sessions after each dosing; primary outcome is change in Y-BOCS-II at 4 days post-second dose with additional follow-up to 12 months and assessment of psychological mediators.
Two psilocybin dosing sessions with preparatory and integration therapy; adaptive second dose.
Second dose adaptive (25 or 30 mg) based on response 4 days after first dose.
7-week waitlist/delayed treatment then same two-dose treatment as immediate group.