Effects of Psilocybin in Obsessive Compulsive Disorder

This study will test the feasibility, safety, and evidence for efficacy of psilocybin administration in participants with obsessive compulsive disorder (OCD). This will serve as a preliminary proof of concept study for future larger studies aimed to investigate the utility, cognitive mechanisms, and neural correlates of this intervention. Participants in this study will receive two doses of psilocybin approximately two weeks apart. Assessments will be conducted during screening visits, psilocybin sessions, and at follow up visits up to 6 months after the final psilocybin session. Thirty participants will complete all study visits including follow-up visits. Primary objectives: 1. Investigate the feasibility, safety, and acceptability of psilocybin for OCD. 2. Investigate the effect of psilocybin on OCD symptoms and concomitant depression and anxiety symptoms. 3. Investigate the effect of psilocybin on quality of life. Secondary objectives: 1. Investigate the effect of psilocybin on metacognition of episodic memory and decision-making. 2. Investigate the effect of psilocybin on model-based learning. 3. Investigate the effect of psilocybin on the ERN. 4. Investigate the effect of psilocybin on affect and social connection. 5. Investigate the effect of psilocybin on movement and communications.