Warfarin is the most commonly prescribed anti-coagulant. It is often given to people with irregular heart beat or people who have suffered a heart attack/stroke or pulmonary embolism. How it works is that it prevents clots from forming or existing clots from growing in you blood vessels. Needless to say, these clots obstruct your blood flow and put your life in peril. Warfarin powerfully decreases these clots, enhances the smooth flow of blood and keeps you healthy.

Vitamin K (phylloquinone) is a vitamin that affects the blood clotting process in our body. Foods rich in vitamin K can reduce the anti-blood clotting effects of Warfarin. Listed below are common food items that may assert a medium to strong influence on the effects of warfarin:

Questions are frequently asked about the interaction between warfarin and herbal medicines. Often, ‘natural’ is regarded as ‘safe’ to most people; unfortunately this is not the case with Warfarin and herbs. There are a host of herbal medicines that possess natural anti-coagulant properties. Taken with warfarin, herbs may have additive effects and increase the potential for bleeding. Others, however, may antogonise the effects of Warfarin.

Below are herbs that increase the anti-coagulant effects of warfarin and cause bleeding:

Listed below are herbs that antogonise the effects of Warfarin, making you more at risk of forming clots:

It is best to avoid ‘coumarin – derivatives’ containing herbal teas as they may also interfere with Warfarin. Examples of these teas include the tonka beans, melot (sweet clover) and sweet woodruff.

Grapefruit juice, a common breakfast beverage in Europe, can adversely affect a drug’s absorption. It can cause a drug to be absorbed from the intestine and reaching toxic levels. Sometimes, it can prevent a drug from working at all. Therefore it is best to avoid eating grapefruit or drinking grapefruit juice 2 hours before or after taking medication. Studies on the interaction between grapefruit juice and Warfarin are inconclusive, so consume this juice with caution when taking Warfarin.

In conclusion, if you are on Warfarin, before taking any herbal, mineral or vitamin supplements, consult a dietitian or pharmacist. Please be warned that some effects may take 2-4 weeks before becoming apparent. It is important to inform your doctor of any changes.

References
1. Booth SL, Sadowski JA, Weibrauch JL, Ferland G. Vitamin K (Phylloquinone) contents of food: A provisional table. J Food Comp Anal 1993; 6: 109-20.

2. Suvarna R, Pirmohamed M, Henderson L. Possible interaction between Warfarin and cranberry juice. BMJ 2003; 327: 1454.

3. Cambria-Kiely JA. Effect of soy milk on Warfarin efficacy. Ann Pharmacother 2002: 36; 1893-6.

4. Stockley IH. Drug Interactions, 5th Edn. London: Pharmaceutical Press, 1999.

5. Makjeha AB. Bailey JM. A platelet phospholipase inhibitor from the medicinal herb feverfew (Tanscetum parthenium) Prostaglandins Leukot Med 1983; 8: 653-660.