Niacin is a B vitamin that's made and used by your body to turn food into energy. It helps keep your nervous system, digestive system and skin healthy.

Niacin (vitamin B-3) is often part of a daily multivitamin, but most people get enough niacin from the food they eat. Foods rich in niacin include yeast, milk, meat, tortillas and cereal grains.

People use prescription niacin (Niacor, Niaspan) to help control their cholesterol.

The recommended daily amount of niacin for adult males is 16 milligrams (mg) a day and for adult women who aren't pregnant, 14 mg a day.

Research on the use of oral niacin to treat specific conditions shows:

• High cholesterol. Prescription niacin is used to increase high-density lipoprotein (HDL) cholesterol — the "good" cholesterol that helps remove low-density lipoprotein (LDL), the "bad" cholesterol, from your bloodstream. Despite niacin's ability to raise HDL, research suggests that niacin therapy isn't linked to lower rates of death, heart attack or stroke.
• Niacin deficiency (pellagra). Niacin and a related nutrient called niacinamide are used to treat or prevent niacin deficiency. This condition isn't common in the United States.

Niacin deficiency has been linked to birth defects. A study in mice suggested that niacin supplementation during gestation prevented birth defects. Research is needed to prove a similar benefit in humans.

When taken orally in appropriate amounts, niacin appears to be safe.

High doses of niacin available via prescription can cause:

• Severe skin flushing combined with dizziness
• Rapid heartbeat
• Itching
• Nausea and vomiting
• Abdominal pain
• Diarrhea
• Gout
• Liver damage
• Diabetes

Serious side effects are most likely if you take between 2,000 to 6,000 mg of niacin a day. If you think you might have overdosed on niacin, seek medical attention immediately.

If you have liver disease, peptic ulcer disease or severe low blood pressure (hypotension), don't take large amounts of niacin. The supplement has been linked with liver damage, can cause hypotension and might activate a peptic ulcer.

Taking niacin also might worsen allergies, gallbladder disease and symptoms of certain thyroid disorders. If you have diabetes, niacin can interfere with blood glucose control. Use niacin with caution if you have the complex form of arthritis gout. Niacin can cause an excess of uric acid in the blood (hyperuricemia), putting you at risk of gout.

If you're pregnant, don't take prescription niacin for high cholesterol. However, if needed to prevent or treat niacin deficiency, niacin is likely safe to take during pregnancy and in breast-feeding women when used in recommended amounts.

Possible interactions include:

• Alcohol. Taking niacin with alcohol might increase the risk of liver damage and worsen niacin side effects, such as flushing and itching.
• Allopurinol (Zyloprim). If you're taking niacin and have gout, you might need to take more of this gout medicine to control your gout.
• Anticoagulant and anti-platelet drugs, herbs and supplements. These types of drugs, herbs and supplements reduce blood clotting. Taking niacin with them might increase your risk of bleeding.
• Blood pressure drugs, herbs and supplements. Niacin might have an additive effect when you take blood pressure drugs, herbs or supplements. This could increase your risk of low blood pressure (hypotension).
• Chromium. Taking niacin with chromium might lower your blood sugar. If you have diabetes and take niacin and chromium, closely monitor your blood sugar levels.
• Diabetes drugs. If you have diabetes, niacin can interfere with blood glucose control. You might need to adjust the dose of your diabetes drugs.
• Hepatotoxic drugs, herbs and supplements. These drugs, herbs and supplements, like niacin, cause liver damage.
• Statins. Research indicates that taking niacin with these cholesterol medications offers little additional benefit when compared with statins alone, and might increase the risk of side effects.
• Zinc. Taking zinc with niacin might worsen niacin side effects, such as flushing and itching.