type of mental disorder in which an individual experiences obsessions or compulsions or both. Either the obsessive thought or the compulsive act may occur singly, or both may appear in sequence.

Obsessions are recurring or persistent thoughts, images, or impulses that, rather than being voluntarily produced, seem to invade a person's consciousness despite his attempts to ignore, suppress, or control them. Obsessional thoughts are frequently morbid, shameful, repugnant, or merely tedious; they are usually experienced as being meaningless and are accompanied by anxiety to a varying degree. Common obsessions include thoughts about committing violent acts, worries about contamination (as by shaking hands with someone), and doubt (as in wondering whether one had turned off the stove before leaving the house).

Obsessions are accompanied by compulsions in approximately 80 percent of cases. Compulsions are urges or impulses to commit repetitive acts that are apparently meaningless, stereotyped, or ritualistic. The compulsive person may be driven to perform the act not as an end in itself but as a means to produce or prevent some other situation, although he is usually aware that the two bear no logical causal relation to each other. Most compulsive acts are rather simple—such as persistent hand washing, counting, checking (e.g., the turned-off stove), touching, or the repetition of stereotyped words or phrases. Occasionally, however, elaborately formalized and time-consuming ceremonials are necessary. The compulsive person usually knows the act to be performed is meaningless, but his failure or refusal to execute it brings on a mounting anxiety that is relieved once the act is performed. Should the sufferer be forcibly or externally prevented from performing the compulsive act, he may experience an overwhelming anxiety.

Obsessive-compulsive disorders affect from two to three percent of the general population, occur equally in males and females, and can first appear at any age. The tricyclic antidepressant (TCA) drug clomipramine (Anafranil) and the selective serotonin reuptake inhibitor (SSRI) fluoxetine (Prozac) (Prozac) have been found to markedly reduce the symptoms in about 60 percent of cases and have thus become the treatment (therapeutics) of choice. Both drugs affect the brain's metabolism of the neurotransmitter serotonin, and this had led researchers to suspect that obsessive-compulsive disorders arise primarily from defects in the brain's neurochemical functioning rather than from purely psychological causes. A drug traditionally used for tuberculosis, d-cycloserine, has also been shown, when used in combination with behavioral therapy, to increase the rate of fear extinction in patients with OCD. The highest rates of the condition occur in high-stress groups, such as those who are young, divorced, or unemployed.