Niacin is likely safe when taken at recommended doses. Pregnant or breast-feeding women should avoid large doses of niacin because there is a lack of safety information for high doses.
At doses higher than 10 mg per day, niacin can cause temporary skin flushing, which may include burning, tingling, itching, headaches, and redness on the face, arms, and chest. Hot drinks or alcohol can make flushing worse when taken with niacin.
Flushing may be reduced by:
- taking acetylsalicylic acid (ASA) or nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen and naproxen before taking each niacin dose
- starting with a small dose of niacin and increasing the dose slowly
Other side effects include gastrointestinal problems such as stomach upset, dizziness, nausea, heartburn, diarrhea, vomiting, and bloating.
Niacin may increase your blood sugar levels. If you have diabetes, check with your health care provider before using niacin. You may need to check your blood sugar more often when using niacin.
Niacin may also increase your risk of bleeding and should be used with caution if you have bleeding disorders or are taking agents that can increase this risk (e.g., anticoagulants, aspirin).
Ask your doctor if you need to have regular liver function tests while you are taking niacin. You should also see your doctor before taking niacin if you have gout, heart disease, gallbladder disease, or low blood pressure.
There may be an interaction between niacin and any of the following:
- anticoagulants (e.g. warfarin, heparin)
- antiplatelets (e.g. clopidogrel)
- blood-pressure-lowering medications (e.g., hydrochlorothiazide)
- bile acid sequestrants (e.g., cholestyramine)
- diabetes medications (e.g., metformin)
- ginkgo biloba
- saw palmetto
- statins (e.g., atorvastatin, fluvastatin)
Stop taking niacin at least 2 weeks before surgery.
Do not use niacin if you have:
- active peptic ulcer disease
- active bleeding
- allergy to niacin or niacinamide
- liver disease
- kidney disease
Before taking any new medications, including natural health products, speak to your physician, pharmacist, or other health care provider. Tell your health care provider about any natural health products you may be taking.