Niacin has been studied in 6 major clinical trials with cardiovascular endpoints. The Coronary Drug Project (CDP) was the largest of these trials and the only one to use niacin monotherapy affecting cardiovascular outcomes: recurrent myocardial infarction and cerebrovascular events were significantly decreased. After long-term (15 years) follow-up, total mortality was also found to be decreased. The other 5 trials used varying combinations of niacin with other pharmacologic agents, examining coronary and total mortality, coronary events, and angiographic progression/regression. Significant benefit was found in all trials except for one in patients with normal cholesterol levels at entry. Thus, the use of niacin to prevent or treat atherosclerotic cardiovascular disease is based on strong and consistent evidence from clinical trials.