Niacin Side Effects: Flushing, Liver Risk and Safe Upper Limits
Why flushing happens
Niacin triggers release of prostaglandins that widen skin vessels, causing warmth, redness and tingling for 15-30 minutes. It is uncomfortable but usually harmless; the NIH ODS niacin fact sheet describes it.
Safe upper limit
For adults, the tolerable upper intake level from supplements and fortified foods is 35 mg daily, set because of flushing. Prescription-level doses used for cholesterol are much higher and need medical supervision.
Other side effects
- Nausea, stomach pain.
- Itching and skin rash.
- Higher blood sugar in people with diabetes.
- Liver injury at high doses.
What to do about a flush
- Take with food.
- Avoid hot drinks and alcohol around the dose.
- Do not double up on supplements with niacin.
- If severe or with chest pain, dizziness or swelling, seek care.
Niacin vs niacinamide
Niacinamide usually does not flush but has different effects. HoneyPezil's list says "niacin"; check the bottle.
Who should ask first
People with liver disease, gout, ulcers, diabetes or who take cholesterol drugs. See the checklist.
Frequently asked questions
Sources
General information, not medical advice. Offer details were checked on November 11, 2026; confirm on the order page and read the label on your bottle. See our disclaimer and how we research.