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