Merck Manual

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Niacin Excess

(Niacin Toxicity; Nicotinic Acid Toxicity)

By

Larry E. Johnson

, MD, PhD, University of Arkansas for Medical Sciences

Last full review/revision Oct 2019| Content last modified Oct 2019
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Niacin (nicotinic acid but not nicotinamide) in high doses may be prescribed to improve cholesterol and triglyceride (lipid) levels in the blood.

Niacin, a B vitamin, is essential for the processing (metabolism) of carbohydrates, fats, and many other substances in the body and for the normal functioning of cells. Good sources of niacin include dried yeast, liver, red meat, poultry, fish, legumes, and whole-grain or enriched cereal products and bread.

The term " niacin" is used in two ways: as a synonym for nicotinic acid and as a broader term that includes nicotinamide and nicotinic acid, two forms of this B vitamin.

High doses of nicotinic acid can have the following beneficial effects:

  • Decrease triglyceride levels

  • Increase high-density lipoprotein (HDL—the good) cholesterol levels

  • Moderately decrease low-density lipoprotein (LDL—the bad) cholesterol levels

However, whether taking nicotinic acid supplements reduces the risk of coronary artery disease and stroke is unclear.

Such high doses of nicotinic acid can cause flushing, itching, gout, and liver damage (rarely) and increase the level of sugar (glucose) in the blood. Flushing may be worse after drinking alcohol, being physically active, being in the sun, and eating spicy foods.

Most side effects can be minimized by starting with a relatively low dose and gradually increasing the dose. Taking aspirin before taking nicotinic acid and taking nicotinic acid after meals also help.

If the side effects of nicotinic acid are intolerable, the dose may be decreased, other (especially extended-release) formulations may be tried, or nicotinic acid may be stopped and another lipid-lowering drug substituted.

Drugs Mentioned In This Article

Generic Name Select Brand Names
No US brand name
NIACOR, NIASPAN
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