Niacin is a vitamin that lowers cholesterol levels. It is also called Vitamin B3 or nicotinic acid. Severe niacin deficiency in the diet can cause a disease called "Pellagra". This is rare in the developed world today. However, less bad deficiency of niacin can cause high blood pressure, weight gain, and hypercholesterolemia. So sometimes Niacin is used to treat hypercholesterolemia. Niacin is one of the medicines that may make HDL (good) cholesterol go up. The biggest problem with taking enough Niacin to help cholesterol is that it causes severe "flushing" (hot, red, sometimes itchy skin). This 'side-effect' is so bad, sometimes people stop taking the medicine.