Foods to Avoid with Coumadin Therapy

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The common anticoagulant medication Coumadin decreases a patient's risk of developing life-threatening blood clots by interfering with clotting factors. Physicians often prescribe the medication for patients with a history of cardiovascular disease. Some foods and beverages interact with the medication, which may decrease the pharmaceutical's effectiveness. Certain food stuffs can also further enhance the anticoagulant effects, which creates a greater likelihood of hemorrhage.

Vitamin K Connection

The fat soluble vitamin is abundantly available in a number of leafy green vegetables. Bacteria in the intestines also manufacture the vitamin. Vitamin K is responsible for making clotting factors II, VII, IX, and X along with other proteins needed for clotting. Coumadin interferes with this process, which slows the time in which blood clotting occurs. However, in order to maintain the correct clotting balance and the international normalized ratio or INR that a physician prefers, patients should not change their vitamin K intake. Unless otherwise directed by a health care provider, individuals taking the medication should continue eating two or three servings of foods containing the vitamin every week. Vitamin K-rich foods include:

• Asparagus
• Beet greens
• Broccoli
• Brussel sprouts
• Cabbage
• Collard greens
• Endive
• Green onions
• Kale
• Mustard greens
• Parsley
• Spinach
• Swiss chard
• Turnip greens
• Canola oil
• Soybean oil
• Mayonnaise


Cranberries and cranberry juice were formerly forbidden to patients taking Coumadin. However, more recent studies concluded that the tart fruit and juice were permitted in amounts of up to eight ounces a day. Excessive amounts enhance the effects of the anticoagulant and elevate INR values.


Grapefruit and grapefruit juice interfere with the metabolism of an enzyme known as CYP3A4, which interferes with vitamin K production in the intestines and in turn enhances the effects of the anticoagulant.

Alcoholic Beverages

Consuming seven or more drinks weekly interferes with fibrinogen, which is also responsible for blood clotting. Drinking while taking Coumadin prolongs the clotting process further and increases the likelihood of suffering from an accidental hemorrhage.

Herbal and Plant Supplements

Patients should avoid starting herbal supplements without the approval of their physician as many formulations increase Coumadin's effects. Products that interact with the anticoagulant include:

• Bromelains
• Coenzyme Q10
Dong quai
• Garlic
• Ginger
• Ginko biloba
• Green tea
• Omega-3 fatty acid supplements
• St. John's wort
• Sweet clover
• Sweet woodruff
• Teas or other products containing tonka beans
• Tumeric

Patients should ensure that they continue getting their blood tested as recommended by their physician. In this way, health care providers are able to make anticoagulant dosage adjustments as needed.

Cite this page: N., Sam M.S., "Foods to Avoid with Coumadin Therapy," in, March 25, 2016, (accessed August 11, 2022).