This clinical trial is investigating whether psilocybin (a psychoactive compound found in certain mushrooms) combined with supportive counseling can help people with treatment-resistant obsessive-compulsive disorder. Researchers will give participants two doses of psilocybin while providing non-directive psychological support to help them process their experiences. The study aims to determine whether this approach is safe, tolerable, and effective at reducing OCD symptoms, and to understand the psychological mechanisms that might explain how it works.