In an effort to prevent and document adverse drug reactions, the University of Southern California Dental School conducted a 2--year study in providing clinical pharmacy services to its patients. The study comprised prescription screening of 2,653 drugs dispensed to 2,418 patients, with 110 reactions being uncovered. These consisted of fifty reports of drug interaction, twenty-nine reports of contraindication, and thirty-one actual cases of side effects. All but the latter group of reactions were avoided by careful review of patients' medical data. The study also discussed the relationship of drug reactions to specific medication prescribed by determining epidemiologic categories of risk.