Psilocybin Whole Mushroom for the Treatment of Obsessive-compulsive Disorder.

This study is testing psilocybin — the active compound from certain mushrooms — as a treatment for obsessive-compulsive disorder (OCD). It is designed for people with moderate to severe OCD who haven't responded well to standard treatments. Participants will receive whole mushroom psilocybin in a supervised clinical setting. **You may be eligible if...** - You are 18 or older - You have been diagnosed with OCD and have at least moderate severity (YBOCS score of 16 or higher) - You have tried at least one standard OCD treatment (like therapy or an antidepressant) without adequate benefit - You can safely live independently **You may NOT be eligible if...** - You have a current substance use disorder or personal or family history of psychosis or bipolar disorder - You have significant heart, kidney, or liver problems - You have attempted suicide in the past 12 months - You are currently taking antidepressants, antipsychotics, or other medications that interact with psilocybin (must be stopped in advance) - You are pregnant, breastfeeding, or planning to become pregnant - You have a weight below 45 kg or are allergic to chocolate or cocoa Talk to your doctor to see if this trial is right for you.