Niacin is used with diet changes (restriction of cholesterol and fat intake) to reduce the amount of cholesterol (a fat-like substance) and other fatty substances in your blood and to increase the amount of high density lipoprotein (HDL; ''good cholesterol''). Niacin can be used in a number of situations including the following: alone or in combination with other medications, such as HMG-CoA inhibitors (statins) or bile acid-binding resins; to decrease the risk of another heart attack in patients with high cholesterol who have had a heart attack; to prevent worsening of atherosclerosis (buildup of cholesterol and fats along the walls of the blood vessels) in patients with high cholesterol and coronary artery disease; to reduce the amount of triglycerides (other fatty substances) in the blood in patients with very high triglycerides who are at risk of pancreatic disease (conditions affecting the pancreas, a gland that produces fluid to break down food and hormones to control blood sugar). Niacin is also used to prevent and treat pellagra (niacin deficiency), a disease caused by inadequate diet and other medical problems. Niacin is a B-complex vitamin. At therapeutic doses, niacin is a cholesterol-lowering medication. Results of a clinical study in people with heart disease and well-controlled cholesterol levels that compared people who took niacin and simvastatin with people who took simvastatin alone and found similar results for the two groups in the rate of heart attacks or strokes. Taking niacin along with simvastatin or lovastatin also has not been shown to reduce the risk of heart disease or death compared with the use of niacin, simvastatin, or lovastatin alone. Talk to your doctor if you have questions about the risks and benefits of treating increased amounts of cholesterol in your blood with niacin and other medications.