The U.S. Food and Drug Administration does not strictly regulate herbs and supplements. There is no guarantee of strength, purity or safety of products, and effects may vary. You should always read product labels. If you have a medical condition, or are taking other drugs, herbs, or supplements, you should speak with a qualified healthcare provider before starting a new therapy. Consult a healthcare provider immediately if you experience side effects.


Avoid in people with known allergy or sensitivity to niacin, niacinamide, or products containing one or both of these products.

Rarely, anaphylactic shock (severe allergic reaction) has been described after giving niacin by mouth or injecting it into the vein.

Side Effects and Warnings

Niacin is likely safe when taken by mouth daily in recommended amounts under the supervision of a qualified healthcare provider. Homocysteine levels should be monitored.

Niacin or niacinamide may result in the following side effects: abnormal heart rhythms, ascites (fluid build-up in the gut lining), blurred vision, build-up of lactic acid in the body, bleeding disorders, changes in liver structure, changes in thyroid hormones, decreased platelets, decreased fibrinogen (chemical that helps clotting), decreased white blood cells, diarrhea, displacement of the eye, dizziness, dry eyes, dry skin, eye disease, eye swelling, eyebrow and eyelash discoloration, failure of blood circulation, fainting, flushing, headache, heartburn, hernia, hypothyroidism (under-active thyroid), increased blood volume in the eye, increased heartbeat, increased creatine kinase, increased homocysteine levels, increased insulin resistance, increased insulin in the blood, increased liver enzymes, increased risk of muscle breakdown, increased uric acid levels in the blood, increased eosinophils (a white blood cell), inflammation of the cornea of the eye, insulin resistance, itching, jaundice (yellowing of the skin), liver adverse effects, liver damage, liver inflammation, liver failure, loss of eyebrows and eyelashes, migraine, muscle disease, nausea, pain in the gums and teeth, panic, peptic ulcer disease, rash, stomach upset, sugar and ketones in the urine, swelling, vision loss due to toxic reactions, vomiting, and warm sensations.

Niacin may increase blood sugar levels. Caution is advised in people with diabetes who are not monitored by a qualified healthcare provider and in those taking drugs, herbs, or supplements that affect blood sugar. Blood sugar levels may need to be monitored by a qualified healthcare professional, including a pharmacist, and medication adjustments may be necessary.

Niacin may increase the risk of bleeding. Caution is advised in people with bleeding disorders or taking drugs that may increase the risk of bleeding. Dosing adjustments may be necessary.

Use cautiously in people with kidney disorders and gout.

Use cautiously in children.

Avoid in people with sensitivity to niacin, niacinamide, or products containing one or both of these products.

Avoid in people with liver dysfunction or disease, peptic ulcer disease, or arterial bleeding.

Pregnancy and Breastfeeding

There is a lack of research regarding the use of niacin during pregnancy and breastfeeding.

This evidence-based monograph was prepared by The Natural Standard Research Collaboration