Simvastatin, a 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitor, has been administered to approximately 2,400 patients with primary hypercholesterolemia with a mean follow-up of 1 year in controlled clinical studies and their open extensions. Approximately 10% of this population received simvastatin for a period of greater than or equal to 2 years. The population on whom this safety analysis is based had a mean age of 50 years; 62% were men and approximately 27% had preexisting coronary artery disease. Simvastatin was titrated to the maximal daily dose of 40 mg each evening in 56% of the study population (last recorded dose). The most frequently reported drug-related clinical adverse experiences were constipation (2.5%), abdominal pain (2.2%), flatulence (2.0%) and headaches (1%). Persistent elevations of serum transaminase levels greater than 3 times the upper limit of normal were observed in only 1% of this cohort with only 0.1% of the total population requiring discontinuation of therapy. There were no clinically apparent episodes of hepatitis. Discontinuation of therapy due to myopathy was extremely rare (0.08%). Only minimal increases in the frequency of lens opacities (1%) were observed from baseline to the last lens examination during follow-up, consistent with the expected increase in lens opacity development due to normal aging. Patients who were greater than or equal to 65 years old had a clinical and laboratory safety profile comparable to the nonelderly population.(ABSTRACT TRUNCATED AT 250 WORDS)