Psychotropic drugs often are helpful in the treatment of selected behavior problems in dogs and cats. Drug therapy is rarely curative by itself and in most cases is only indicated as ancillary therapy in a behavior modification program. Very few of the psychoactive drugs are approved for use in companion animals, and owners should be made aware that their use is considered experimental. Before prescribing any of the psychotropic drugs, veterinarians should be thoroughly familiar with dosages, side effects, and contraindications. Some of the more common behavior problems in which drug therapy may be useful are reviewed.