The lifetime prevalence estimate of obsessive–compulsive disorder (OCD) is approximately 2–3% in the US and worldwide.^1–3 The manifestation of OCD includes intrusive unwanted thoughts (i.e. obsessions) and repetitive behaviors (i.e. compulsions).⁴ Obsessions are thoughts, images, or impulses that occur over and over again and that feel out of control. These obsessive thoughts are unwanted (dystonic) and are usually experienced as disturbing and intrusive. Common obsessions include contamination fears (of germs, chemicals, bodily fluids, etc.), pathological doubting (e.g. imagining having harmed someone, having said the wrong thing, having not locked doors, etc.), intrusive violent or sexual thoughts or urges, concerns with symmetry or ordering, and religious scrupulosity. Compulsions are behaviors that the person performs over and over again, usually in response to obsessions. Individuals with OCD perform these compulsions in response to and in order to minimize their obsessions. Unfortunately, the obsessions return and the OCD sufferer repeatedly experiences obsessions and performs compulsions. Common compulsions include repeated washing, cleaning, checking, touching, counting, and arranging behaviors. Most OCD sufferers have multiple obsessions and multiple compulsions.³ Everyone experiences occasional unwanted thoughts, performs occasional repetitive or ritualistic behaviors, and has occasional transient feelings of anxiety; in order to meet the criteria for OCD, the obsession and compulsions must be sufficiently intense or frequent to cause marked distress or impair functioning. Many people with OCD are severely impaired by the symptoms of their disease, with many performing rituals for hours each day; some may become housebound due to avoidance. This, of course, can result in severe socioeconomic difficulties. Most people with OCD recognize that their thoughts and behaviors are extreme or nonsensical (i.e. they have insight into their symptoms) and are often embarrassed or ashamed of their condition and frightened that they may be ‘going crazy.’

Unfortunately, many patients with OCD are not diagnosed properly and may not receive adequate treatment. The most important factor in successfully treating OCD is correctly diagnosing OCD. While a thorough clinical evaluation should result in the correct diagnosis in the majority of cases, it is important to consider the differential diagnosis (including ruminations of major depression, racing thoughts of mania, and delusional thoughts of psychosis). Also, comorbid diagnoses—especially mood and anxiety disorders—are common in patients with OCD and adequate treatment of these comorbid conditions is essential. If treatment of comorbid conditions is suboptimal, their associated symptoms may interfere with the treatment of the OCD symptoms. It is important that both the treater and the patient understand what is considered response to treatment for OCD. The gold standard for assessing the severity of OCD symptoms is the Yale–Brown Obsessive Compulsive Scale (Y-BOCS),^5,6 a clinician-administered scale that assesses the frequency, interference, distress, resistance, and control of both obsessions and compulsions. The majority of pharmacotherapy trials for OCD have used a reduction of 25–35% of Y-BOCS scores from baseline as the definition of response. Therefore, it is important to recognize that many patients who are characterized as responders will often still have significant residual symptoms. Lastly, while this article focuses on pharmacotherapy for OCD, behavioral therapy—specifically exposure and response prevention (ERP)—is also highly effective and is often used instead of or in conjunction with pharmacotherapy.

Serotonin Re-uptake Inhibitors
The first-line pharmacotherapy treatment for OCD is the serotonin re-uptake inhibitors (SRIs), despite not all of them having a specific US Food and Drug Administration (FDA) indication for the treatment of OCD. The SRIs include all of the selective SRIs (SSRIs)—fluoxetine (Prozac), sertraline (Zoloft), paroxetine (Paxil), fluvoxamine (Luvox), citalopram (Celexa), and escitalopram (Lexapro)—as well as clomipramine (Anafranil), a tricyclic antidepressant with a mechanism of action that primarily involves serotonin re-uptake inhibition. The efficacy of the SRIs for the treatment of OCD has been demonstrated by a large number of randomized, double-blind, placebo-controlled trials.^7–12 A meta-analysis of these trials found that in most studies 40–60% of patients respond to the SRIs with a 20–40% mean decrease in OCD symptoms.¹³ Head-to-head trials between different SRIs for the treatment of OCD suggest that no one SRI is more efficacious than the others for the treatment of OCD.¹⁴ However, controlled head-to-head trials of SRIs and tricyclic antidepressants in the treatment of OCD have demonstrated that SRIs are more efficacious than tricyclic antidepressants (other than clomipramine)

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