The authors report a meta-analysis of 32 years of prospective studies on adverse drug reactions (ADRs). The study specifically excludes medication ordering or administration errors, focusing instead on drug toxicity, allergic reactions, and idiosyncratic adverse reactions. The authors estimate an overall incidence of 6.7% for serious ADRs in hospitalized patients and 0.32% for fatal ADRs. Using 1994 as a representative year, the authors calculate an estimated 2,216,000 serious ADRs in the United States for that year, with 106,000 fatalities, an estimate that would make ADRs between the fourth and sixth leading causes of death in the United States.