Mental disorder in which an individual experiences obsessions or compulsions, either singly or together. An obsession is a persistent disturbing preoccupation with an unreasonable idea or feeling (such as of being contaminated through shaking hands with someone). A compulsion is an irresistible impulse to perform an irrational act (such as repeatedly washing the hands). The two phenomena are usually, but not always, linked in the obsessive-compulsive person. Onset of the illness has been linked to malregulation of the neurotransmitter serotonin as well as to the ill effects of high stress.

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