In this review all twenty controlled studies, dealing with antidepressant therapy on OCD are discussed. Although many different drugs have been documented best. Using this drug four to eight weeks, about 50% of the patients show a symptom reduction averaging 40%. None of them recovers completely. After tapering off the medication all patients show a complete relapse. During treatment most patients complain of anticholinergic symptoms and psychosexual dysfunction, leading to a drop-out rate of 20%. The anti-obsessive effect is independent of the severity of the depression. Clinical research of clomipramine in obsessive-compulsive disorder, has led to the `serotonin hypothesis' of the syndrome.