Supplements That Interfere With Coumadin

Also known as warfarin, Coumadin is a medication your physician prescribes to prevent life-threatening blood clots from forming. While the medication can help you to stay healthy, it relies on a delicate balance in your blood to prove effective. This means taking certain supplements with Coumadin can increase your risk for experiencing harmful effects, including increased risk for bleeding. Always disclose all supplements -- including herbal pills and vitamins -- you are currently taking to your physician.

Affects Absorption

Certain supplements affect the rate at which your body absorbs Coumadin. This means your body does not take in as much of the medication as it typically does, which can affect how well your medication works. To prevent this, you should avoid taking supplements like green tea, coenzyme Q10, iron, magnesium, St. John’s wort, vitamin C and zinc, according to True Star Health.

Harmful Interactions

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Other supplements can interfere with Coumadin to cause harmful drug interactions that increase your risk of bleeding to causing dizziness, weakness or headache (see reference 3). A variety of supplements, especially herbal supplements, can potentially interact negatively with Coumadin. This includes American ginseng, devil’s claw, fenugreek, garlic, ginger, ginkgo biloba, quinine, red clover or sweet woodruff, according to True Star Health. Vitamin D supplements also can interact harmfully with taking Coumadin.

Varying Dosages

Some supplements are known to put you at increased risk for experiencing a harmful interaction with Coumadin. This includes supplements like bromelain and eleuthero, according to True Star Health. Taking extra vitamins such as vitamins C and E also may increase your risk for harmful drug interactions with Coumadin. Taking vitamin K also can be dangerous when you are taking Coumadin because vitamin K can interfere with how Coumadin works. This is because vitamin K is a vitamin that contributes to blood clotting.


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If you do take a supplement known to interact with Coumadin, contact your physician to determine the next dosage or potential side effects related to taking the medication. Seek emergency medical attention if you experience side effects such as severe bleeding, black stools, body swelling, chest pain, difficulty moving or numbness or tingling in any part of your body, according to