A single dose of psilocybin (0.25 mg/kg) produced rapid, clinically meaningful, and sustained reductions in obsessive-compulsive disorder (OCD) symptoms among adults with treatment-resistant OCD. In a randomized, double-blind, placebo-controlled trial, the psilocybin group showed a 9.76-point decrease on the A-YBOCS at 48 hours, compared to a 0.07-point increase in the niacin group. At one week, 69.2% of psilocybin participants achieved a response (≥35% symptom reduction) versus 0% of niacin participants. Benefits persisted through 12 weeks. One serious adverse event (suicidal ideation) occurred; no treatment-related deaths were reported.
In people with treatment-resistant obsessive-compulsive disorder (OCD), greater mystical-type experiences during psilocybin sessions—especially feelings of unity, sacredness, and transcendence—were linked to lower OCD symptom severity at 1-week and 12-week follow-ups, even after accounting for baseline severity and treatment condition. The Mystical subscale of the Mystical Experience Questionnaire showed the strongest and most consistent associations. The Space–Time subscale was related to lower OCD severity only at 12 weeks. Positive mood, ineffability, and challenging experiences were not significantly tied to post-treatment OCD severity. These results suggest that the quality of subjective experience during psilocybin sessions may help optimize treatment outcomes.