Effects of Ondansetron in Obsessive-compulsive and Tic Disorders

This project investigates the use of 4 weeks of 24 mg/day ondansetron as compared to placebo on symptoms and brain functioning in patients with obsessive-compulsive disorder (OCD) and tic disorders (TD). Patients will be randomized to receive ondansetron or placebo for 4 weeks, with MRI scans and symptom assessments occurring at baseline (before any drug) and at the end of the 4 weeks. Patients will also be asked to come into the lab approximately 2 weeks into the trial for symptom assessments. The investigators hypothesize that after 4 weeks there will be greater reduction from baseline in sensory symptoms and the activation of the insula and sensorimotor cortex compared for ondansetron as compared to placebo.