Say no to niacin? - side effects of high doses of niacin

Harvard Health Letter, June, 1994

Some medical self-help books make niacin sound like a panacea for health-conscious people with rising cholesterol levels and shrinking budgets. Because this B vitamin is cheap and sold over-the-counter at drug and health food stores, people see no reason to check with the doctor before tossing back a handful of pills. What they may not know is that the high doses (1,500-3,000 mg) needed to lower cholesterol levels can cause serious complications. (As a dietary supplement, 10-20 mg is usually recommended). To add to the confusion, niacin comes in two forms: immediate- and sustained-release preparations.

The results of a recent study from the Medical College of Virginia and the University of Pennsylvania College of Medicine highlight the differences between the two forms and show that the adverse effects of sustained-release niacin can be dangerous as well as annoying.

Participants in this study gradually increased their daily intake of niacin from 250 mg to 3,000 mg over 36 weeks. Nine of the 23 people who were taking immediate-release niacin withdrew from the study early because of facial flushing, fatigue, or skin discoloration. Eighteen of the 23 who were taking 3,000 mg daily of sustained-release niacin dropped out due to upset stomachs, fatigue, or abnormal liver function tests. All of these side effects disappeared once the participants stopped taking the vitamin. Additional cause for concern comes from other reports suggesting that high doses of sustained-release niacin can cause jaundice and liver failure.

But researchers emphasize that immediate-release niacin should remain as a treatment option for high cholesterol. "The point of our study is not that niacin should be avoided, but that the immediate-release preparation is the preferred form, and that medical supervision and evaluation are necessary for people taking this drug," said James McKenney, professor and chairman of the division of clinical pharmacy at the Medical College of Virginia.

It's especially important for people taking high doses of niacin to have regular liver function tests. These should be performed every few weeks when a patient is adjusting to a new dose, and after that can be cut back to once or twice a year, said Dr. McKenney.

"People should make sure that they stick with the same brand of niacin because side effects may vary from one manufacturer to the next," advised Mason Freeman, director of the Lipid Clinic at Massachusetts General Hospital.