Inclusion criteria required that subjects, ages 14-70 years, have at least a 1-year duration of a current Diagnostic and Statistical Manual of Mental Disorders-IV (DSM-IV) principal diagnosis of OCD. Furthermore, the OCD had to be defined by a rating of "moderate" or greater on the global severity item of the Clinical Global Impressions (CGI) scale and have a Yale-Brown Obsessive Compulsive Scale (Y-BOCS) score of 19 or greater.

Exclusion criteria included primary depression, schizophrenia, or other psychotic disorders; active bipolar disorder; abuse of alcohol or other significant substance within 6 months; increased risk of seizures or history of neurosurgery, encephalitis, or significant head trauma; or a significant medical condition, such as heart, liver, or renal disease. Subjects with an intelligence quotient of less than 80 as determined with the Kaufman Brief Intelligence Test (Kaufman and Kaufman 1990) were excluded.