Effects of psychotropic drugs on intelligence test performance of institutionalized mentally retarded adults

Twenty-four institutionalized mentally retarded persons received intelligence tests under both standard and reinforcement conditions while on and off psychotropic medication. Medications included chlorpromazine (Thorazine), thioridazine (Mellaril), haloperidol (Haldol), mesoridazine (Serentil), and lithium carbonate (Lithane). Results showed that when on medication there were no differences between IQs obtained under standard and reinforcement conditions. When off medication there were significant increases in scores obtained under both standard and reinforcement conditions. The increase in scores under the reinforcement condition was 23 points greater than the increase obtained under the standard condition (increases of 30.2 and 6.9 points, respectively). Results were discussed in terms of the sensitivity--insensitivity of intelligence test scores to medication effects, medications impairing responding to external reinforcement contingencies, and legal implications.