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

Eligibility Criteria for Participants with OCD: Who May Qualify: - 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 willing to sign a consent form Who Should NOT Join This Trial: - 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: Who May Qualify: - Ages 18-65 - Able to provide willing to sign a consent form Who Should NOT Join This Trial: - current or past use of psychotropic medication - pregnant or nursing females - the presence of metal in the body that is contraindicated for MRI scans Always talk to your doctor about whether this trial is right for you.