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

Eligibility Criteria for Participants with OCD: Inclusion Criteria: * Ages 18-65 * Meet the criteria for OCD diagnosis * Failed at least 1 prior trial of standard first-line OCD treatment * Agree to the following lifestyle modifications: comply with requirements for fasting prior to the Experimental Session, not enroll in any other interventional clinical trials during the duration of the study, and commit to medication study procedures. * Able to provide informed consent Exclusion Criteria: * prior naltrexone or ketamine use/exposure * Any current or past medical/psychiatric condition that makes participation unsafe in the opinion of the investigator or study physician * Pregnant or nursing, or able to become pregnant and are not practicing an effective means of birth control * the presence of metal in the body that is contraindicated for MRI scans Eligibility Criteria for Healthy Volunteers: Inclusion Criteria: * Ages 18-65 * Able to provide informed consent Exclusion Criteria: * current or past use of psychotropic medication * pregnant or nursing females * the presence of metal in the body that is contraindicated for MRI scans