Safety and side effects

Experts believe niacin to be safe when taken by mouth in typical amounts.

High doses of prescription niacin can cause:

• Skin flushing and dizziness.
• Itching.
• Upset stomach and vomiting.
• Belly pain.
• Loose stools.
• Gout.
• Liver damage.
• Diabetes.

Serious side effects are likely for people who take between 2,000 and 6,000 mg of niacin a day. If you think you might have taken too much niacin, seek medical help right away.

If you have a liver condition, a peptic ulcer, or very low blood pressure, called hypotension, don't take large amounts of niacin. The supplement has been linked with liver damage. Liver damage can cause hypotension and might make a peptic ulcer active.

Taking niacin also might make allergies, gallbladder conditions, and symptoms of some thyroid conditions worse. If you have diabetes, niacin can affect how you manage your blood sugar. Use niacin with care if you have gout. Niacin can cause too much uric acid in the blood, called hyperuricemia. This raises the risk of gout.

If you're pregnant, don't take prescription niacin for high cholesterol. But if you need niacin to prevent or treat lack of niacin, called deficiency, niacin is likely safe to take during pregnancy and breastfeeding. Use it only as your healthcare professional tells you.