Fenofibrate is a fibric acid derivative with enhanced potency and specificity of action on lipids. Preclinical toxicology reveals minimal toxic effects; dose-related changes occurred seldom, with only hepatic effects in rodents (mainly enzyme changes), some renal effects in dogs, and no reactions in monkeys. Teratogenicity tests were negative, and mutagenicity was not associated with fenofibrate. Carcinogenicity was evident in rodents with liver carcinoma at doses of 12 or 40 times the human dose, but cancer has not been associated with fenofibrate in over 10 years of clinical research and use. European experience with fenofibrate involved 7,145 patients in short- and long-term clinical trials, plus 10 years of marketing experience with a patient exposure of 6 million patient-years. Adverse effects were relatively low in frequency (6%) in the European clinical trials and manifested as gastrointestinal effects, muscle pain, skin problems, and sweating or dizziness. Short- and long-term fenofibrate studies revealed basically the same scope and frequency of adverse effects. Experience in US clinical trials mirrored the European experience; three types of adverse effects occurred more commonly in fenofibrate patients versus placebo: skin reactions, neurologic effects, and musculoskeletal reactions. Laboratory tests were mildly abnormal for liver function, leukocytes, and hemoglobin; these reactions were significant enough to be considered adverse drug experiences only occasionally. Hepatobiliary tests for lithogenicity showed an increase in cholesterol saturation, but gallstones seldom have been associated with fenofibrate. Postmarketing, open experiences in Europe over 10 years have been consistent with the study results. The rate of reactions has been low (about 115/year or a 0.3% incidence rate). The reactions noted in these spontaneous reports were hepatic, renal, gallstones, cutaneous, hematologic, sexual asthenia, and weight loss. In general, fenofibrate can be considered a safe and well-tolerated lipid-lowering drug that has been scrutinized extensively for safety in clinical research and during an already long marketing period in Europe.