It was not until 1967 that the tricyclic antidepressant clomipramine, the first available serotonin reuptake inhibitor（SRI）,emerged as an effective treatment for obsessive-compulsive disorder（OCD）. Subsequently, the efficacy of selective serotonin reuptake inhibitors （SSRIs）for OCD has been demonstrated in many studies. From these findings, neurochemical dysfunction in the serotonin system has been implicated in OCD pathogenesis. However,as many as half of OCD patients treated with an adequate trial of SRIs fail to fully respond to treatment and continue to exhibit significant symptoms. Hence, there is often a need to augment SRI treatment with other drugs. Currently,the best existing evidence favors antipsychotic drugs.
 Although much of the emphasis of pathophysiologic theories of OCD has been on serotonin,a growing body of evidence supports a role for dopaminergic neurotransmission in this disorder. At the same time, a range of functional neuroimaging studies have pointed to involvement of the cortico-basal ganglia loop（the “OCD loop”）in OCD. Effective pharmacotherapy is likely to modulate the OCD loop, thereby regulating functioning within the serotonin and dopamine neurotransmitter systems.