Examining Mu Opioid Mechanisms of Ketamine's Rapid Effects in OCD (MKET2)

This study is investigating whether the rapid antidepressant effects of ketamine (an anesthetic sometimes used for depression) in people with OCD (obsessive-compulsive disorder) are related to the opioid system in the brain. **You may be eligible if...** - You are between 18 and 65 years old - You have a confirmed diagnosis of OCD - Standard first-line treatments (such as therapy or certain medications) have not worked for you — you must have tried at least one - You are willing to fast before the experimental sessions - You are able to follow the study requirements **You may NOT be eligible if...** - You have a current substance use disorder or history of opioid use - You have certain other psychiatric conditions that could interfere with the study - You are pregnant or breastfeeding - You have serious medical conditions affecting the heart, liver, or kidneys - You are taking medications that interact with ketamine or naltrexone Talk to your doctor to see if this trial is right for you.