Ondansetron in Treatment Resistant Obsessive Compulsive Disorder (OCD)

Inclusion Criteria: 1. adults aged 18 to 55 2. a Yale-Brown Obsessive-Compulsive Scale (Y-BOCS) score of ≥ 20 after ≥ 12 weeks of treatment with an established effective dose of an Selective Serotonin Reuptake Inhibitors or clomipramine and after ≥ 10 weeks of augmentation treatment with antipsychotics (risperidone at least 2 mg/day quetiapine at least 150 mg/day; olanzapine at least 5mg/day; haloperidol titrated at least 10 mg/day; aripiprazole at least 10 mg/day) Exclusion Criteria: 1. a history of alcohol or substance abuse 2. current severe depressive symptoms, bipolar disorder, panic disorder, schizophrenia, or other psychiatric conditions 3. heart disease, arrhythmia, liver problems, including cirrhosis, seizures, glaucoma or serious medical disease 4. hoarding as only Obsessive Compulsive symptom 5. women of childbearing potential not using a medically acceptable contraceptive method.