Niacin The mechanism of action of niacin is not fully understood, but it appears to inhibit the secretion of lipoproteins containing apo B100 from the liver. Niacin decreases both total and LDL cholesterol approximately 15 to 25%, reduces VLDL levels by 25 to 35%, and raises HDL cholesterol levels by as much as 15 to 25%. Thus, niacin exerts favorable changes on the three major lipoproteins (VLDL, LDL, and HDL). Efficacy of monotherapy was confirmed in a longterm secondary prevention trial in which niacin significantly reduced the incidence of myocardial infarction. An even longer-term follow-up of that study (15 years total) showed an 11% decrease in all-cause mortality among patients randomized to niacin. Because of its ability to reduce VLDL synthesis, niacin is also a first-line drug for treatment of hypertriglyceridemia.