Efficacy of Adding Topiramate to Current Treatment in Refractory Obsessive Compulsive Disorder (OCD)

Inclusion Criteria: * Outpatient with primary DSM- IV OCD * Completion of a 14-week open label trial of one the following SRI's: fluoxetine 80 mg/day, paroxetine 60 mg/day, fluvoxamine 300 mg/day, clomipramine 250 mg/day, sertraline 200 mg/day, citalopram 60 mg/day, escitalopram 30 mg/day and demonstrating a non or partial responses to SRI treatment (CGI-I of 3 or 4, Y-BOCS reduction of \< 35%) * Stable (8 wks or longer) concurrent medications including benzodiazepines, sedative hypnotics, antipsychotics, and antidepressants. Exclusion Criteria: * Any other primary DSM-IV diagnosis; DSM-IV criteria for body dysmorphic disorder, bipolar affective disorder, schizophrenia, psychotic disorder, current alcohol/substance abuse. * A previous adequate trial of topiramate * Comorbid major depressive disorder diagnosis which predates OCD diagnosis * Cognitive behavioural therapy or additional psychotherapy in past four months * Allergy or hypersensitivity to topiramate * BMI \< 20 * History of kidney stones