Warfarin is a medication used to help prevent and treat blood clots. The drug is often referred to as a blood thinner. People who have a history of blood clots or an increased risk for stroke are among those who use warfarin. Like other types of medication, the foods and drinks you consume may alter the way warfarin works in your body. Speak to your doctor about your diet to determine which foods you, personally, should avoid.
Leafy green vegetables, including spinach, kale, Swiss chard, mustard and collard greens are all high in vitamin K. Vitamin K is an essential part of the blood clotting process, and eating too much of the nutrient can compromise the efficacy of warfarin. You do not necessarily need to avoid all foods that contain vitamin K, but you should be vigilant about how much of the vitamin you consume. A half-cup serving of these leafy green vegetables can give you up to 600 percent of the daily recommended allowance of vitamin K. The RDA for men for vitamin K is 120 mcg and 90 mcg for women. Consuming more than six times this amount may be too much when you are also taking warfarin. Avoid eating large servings of leafy greens on a regular basis.
Broccoli, Brussels sprouts and cabbage, otherwise known as cruciferous vegetables, are also high in vitamin K and should be avoided on a daily basis. Even for people taking warfarin, vitamin K is an essential nutrient, so speak to your doctor before cutting out these foods completely. If your medical care provider feels your warfarin is not as effective as if should be due to your diet, try making substitutions. Add cauliflower to a stir fry, for example. Use lettuce instead of cabbage in salads. Romaine and green leaf lettuce are considered moderate sources of vitamin K.
Alcohol can increase the effectiveness of warfarin, making the drug work too well, so to speak. In other words, your blood might not clot when it is supposed to after an injury. The risk of bleeding is heightened when you combine large amounts of alcohol with warfarin. Drinking more than three alcoholic beverages daily is not advised. One "drink" equals 12 oz. of beer, one 1.5 oz. shot of hard liquor or 5 oz. of wine.
Green tea is also a source of vitamin K and should be consumed with care; consult your doctor if you normally drink large quantities of the antioxidant-rich tea and are prescribed warfarin. Cranberry juice is another beverage that can negatively interfere with the blood thinner. This juice may decrease the effectiveness of blood thinning drugs on the ability of your blood to clot. Simply said, drinking more than 8 oz. of cranberry juice daily can slow down the effect of warfarin, putting you at higher risk for problems. Grapefruit or grapfruit juice may also cause your body to absorb too much warfarin. If you are unsure whether grapefruit is safe for you, check with you doctor.
- U.S. Food and Drug Administration -- Medication Guide: Coumadin
- National Institutes of Health -- Important Information to Know When You Are Taking Coumadin and Vitamin K
- Stanford Primary Care Clinics: Warafin Instruction Sheet
- U.S. Department of Health and Human Services: Drug Interaction Report -- Warafin Sodium with Food