Safety and side effects

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.