The Gut Microbiota in Obsessive-Compulsive Disorder

Eligibility Details: Inclusion Criteria: - Patients with a primary diagnosis of OCD (DSM 5) according to the MINI - Y-BOCS score of ≥20. - MADRS < 18 Exclusion Criteria: - Participants with current Major Depressive Disorder. - Patients with significant suicidal ideation (MADRS item 10 ≥ 3) or who have enacted suicidal behaviors within 6 months prior to intake will be excluded from study participation and referred for appropriate clinical intervention. - Individuals with current autoimmune disorders (rheumatoid arthritis, systemic lupus erythematosus, multiple sclerosis, etc.), inflammatory bowel disease, diabetes. - Current use of any psychotropic agent SSRIs, benzodiazepines, MAO Inhibitors, tricyclic antidepressants. Past pharmacotherapy is permitted if treatment ended 3 months prior to sampling. - Current use of herbal psychoactive treatments i.e. St. John's Wort, Kava Kava, Chamomile Extract, Valeria. Past use is permitted if treatment ended 3 months prior to sampling. - Participants receiving current psychotherapy, including cognitive behavioural therapy for an anxiety or mood disorder 3 months prior to sampling. - Patients who currently fulfill criteria for a lifetime history of bipolar disorder, history of drug abuse, a history of schizophrenia or other psychotic disorders, delirium, dementia and amnesic and other cognitive disorders, or are in a current agitated state. - Patients meeting criteria for current substance use disorder. - A body mass index (BMI) >30 - Antibiotic or probiotic use within 8 weeks of sampling. Patients beginning antibiotic treatment or probiotic use during Phase II of the study will be excluded.