• ≥ 22 years and ≤ 75 years of age, at the time of screening

• Chronic (\> 5 years preceding the date of enrollment) OCD, diagnosed as per the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition guidelines (DSM-5)

∙ Presence of obsessions, compulsions, or both

‣ Time-consuming obsessions and compulsions that take more than one hour a day or cause clinically significant distress or impairment in social, occupational, or other important areas of functioning

‣ Obsessive-compulsive symptoms that are not attributable to the physiological effects of a substance (e.g. a drug of abuse, a medication) or another medical condition

‣ Disturbance not better explained by the symptoms of another mental disorder listed in the DSM-5

• Severe OCD symptoms, as defined by Y-BOCS I score of ≥ 28, within two weeks prior to enrollment

• Lack of adequate response to a history of the following treatments, based on information from any of the following: (a) the current treating physician and/or psychologist; (b) medical records or other forms of communication from previous healthcare providers; and (c) pharmacy records, as determined by the Principal Investigator

∙ Adequate trial of ≥ 2 selective serotonin reuptake inhibitors (SSRIs) for an adequate duration at the maximum dose recommended for OCD or at the maximally-tolerated dose according to the FDA-approved package labeling

‣ Adequate trial of ≥ 1 augmentation trial using an antipsychotic medication

‣ Adequate trial of clomipramine, either as monotherapy or as an augmentation therapy, unless medically contradicted

‣ Adequate trials of cognitive behavior therapy-based Exposure and Response Prevention (ERP)

• Willingness and ability to remain on the same daily dose of any and all scheduled psychotropic medication(s) for at least 8 weeks prior to study enrollment and for the duration of the trial, in the opinion of the Principal Investigator

• Willingness and ability to discontinue any psychotherapeutic behavioral intervention therapy (e.g. CBT) until the maintenance stage, if determined safe by the research/study psychiatrist

• Study participation in the prospective subject's best psychiatric interest, as determined by the research/study psychiatrist and based on a comprehensive assessment that includes the following: (a) detailed psychiatric history; (b) examination of the mental status; (c) review of psychiatric assessment measures obtained to determine eligibility, as applicable; (d) review of previous medical records for a minimum of 2 years prior to enrollment, or as applicable; and (e) consideration of the potential benefits versus risks of study participation

• Agreement to being evaluated by a licensed psychiatrist and/or psychologist at regular intervals, as required by the schedule of events, for the duration of study participation

• Living within 6 hours of driving distance from study sites and no plan of relocation for at least the duration of the trial (approximately 18-24 months), as reported by the prospective subject or a family member

⁃ Adequate social support, including but not limited to, stable housing and two family members and/or friends, who are identified as a verifiable emergency contacts

⁃ Willingness and ability to provide at least two verifiable contacts for emergency purposes and to permit verification of emergency contacts by research staff before all study visits and as needed, at the discretion of the Principal Investigator

⁃ Ability to understand procedure-related instructions and to complete study assessments in English, in the opinion of the Principal Investigator

⁃ Willingness and ability to comply with protocol requirements (e.g. procedure visits, treatment schedule, follow-up visit schedule, evaluations, etc.), in the opinion of the Principal Investigator

⁃ Willingness and ability to provide written agreement to allow any and all forms of communication between the research team and treating clinician(s)

⁃ Willingness and ability to provide informed consent, in the opinion of the Principal Investigator