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Interactions With Niacin & Warfarin

By M. Gideon Hoyle

Niacin, or vitamin B-3, is one of the B complex vitamins. All the B vitamins help convert carbohydrates into glucose to produce energy. Niacin also aids in the production of various hormones and is effective in improving circulation and reducing cholesterol levels in the blood. If you take blood-thinning medications including warfarin, you should consult your doctor before taking niacin.


Niacin as present in a variety of foods, including peanuts, beets, tuna, sunflower seeds, swordfish, beef liver and brewer’s yeast, as well as niacin-fortified cereals and breads. Standard and timed-release niacin supplements come in both tablet and capsule form. Most people get enough B-3 from dietary sources and have no need for supplementation, according to the University of Maryland Medical Center (UMMC). Niacin is used in high dosages to treat high cholesterol.


Warfarin, commercially available as Coumadin and Jantoven, is commonly used to stop clots from forming in your bloodstream, or to stop existing clots from increasing in size. It achieves these effects by interfering with your body’s ability to produce specialized substances called clotting factors. Your doctor may prescribe a warfarin-based product in the aftermath of a heart attack, if you have specific types of irregular heartbeat or if you undergo any form of heart valve replacement. Additional uses of the drug include treatment and prevention of blood clots in your lungs and treatment and prevention of clots and swelling in veins located elsewhere in your body.

Interaction Risks

By itself, warfarin can trigger severe bleeding problems that can threaten your life or result in death. Apart from potential interactions with other medications or supplements, people using this drug must monitor themselves for any signs or symptoms of bleeding-related problems. When used simultaneously with warfarin, niacin can potentially intensify this medication’s anti-clotting effects, in addition to increasing your risks for bleeding-related side effects. If you take warfarin or any other blood-thinning medication, don’t take niacin in any form without getting prior consent from your doctor.

Additional Risks

When used in doses high enough to lower your cholesterol or produce other therapeutic results, niacin carries additional risks that include stomach ulcers and liver damage. If you have a known history of either ulcers or liver problems, you should avoid taking niacin. In addition to niacin, medications that can cause dangerous interaction in combination warfarin include ibuprofen, naproxen, aspirin and a wide variety of drugs used to treat conditions such as heart disease, high cholesterol, depression, mental illness, diabetes, seizures and cancer. Due to the sheer number of products that can alter warfarin’s effects, make sure to discuss all medications and supplements with your doctor before you use them.

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