This study will examine the efficacy of pregabalin (Lyrica) added to serotonin-reuptake inhibitor (SRI) treatment in obsessive-compulsive disorder (OCD) for individuals who have not responded or only partially responded to an adequate trial of an SRI. Although SRIs have demonstrated efficacy in OCD in numerous placebo-controlled trials, response rates have been as low as 40%. Augmentation strategies (adding an another medication) would be beneficial to maximize treatment response in OCD. The study will consist of patients who have not attained full response to an SRI. The patients will be randomized in a double-blind fashion to the addition of pregabalin (Lyrica) or placebo to the regular dose of SRI. At the end of the study, particpants will enter follow-up care with the study doctor.