Warfarin is a drug used to prevent blood clots from occurring and to prevent already formed clots from getting bigger.1 It works by prolonging the time required for blood to clot.2 Having a balanced diet is always something important to consider; however, when taking warfarin, deciding on what food you eat becomes more important than just a consideration.
1. Warfarin and Foods that Contain Vitamin K
- Vitamin K plays an important role in blood clotting.2
- Eating larger than normal amounts of vitamin K-containing foods can work against warfarin’s effects by lowering the time required for a clot to form, making warfarin less effective.2
- For warfarin to maintain proper function, the level of vitamin K in the body must be kept constant.2 If your vitamin K levels are frequently changing, it could alter the effects of warfarin and potentially increase risk of complications such as blood clots.1
- Be aware of foods containing vitamin K. Leafy green vegetables (e.g., kale, broccoli, spinach, collard or turnip greens, and Brussels sprouts) have some of the highest vitamin K levels in food.1,2 Speak to your pharmacist to learn more about how much vitamin K is contained in various foods.
- Rather than avoiding these foods, patients should aim to consume relatively similar amounts of vitamin K contained in foods each week and avoid large day-to-day variations.2 For example, try to keep daily meals consistent (e.g., salad at lunch, cooked green vegetables at dinner).3 If you are unable to have similar daily meals, try to keep them similar weekly (e.g., 3 or 4 days each week of green vegetables at dinner).
- Recognize common circumstances that can cause a change in dietary vitamin K levels such as3:
- Eating more green vegetables than usual
- Having the flu and not eating routinely
- Being admitted to the hospital on a limited diet
- Consuming different foods while travelling
2. Warfarin and Other Foods:
- There are additional foods that, although contain very low levels of vitamin K, may still prevent warfarin from working properly.2
- For example, if you consume cranberry juice, brewed green tea, grapefruit, and/or grapefruit juice, you may have to limit the amount to 1 to 2 servings per day.2
- Note: This list is not inclusive of all foods. Speak to your pharmacist for more information about food interactions with warfarin.
3. Warfarin and Alcohol
- Consuming too much alcohol while taking warfarin can increase your risk of bleeding.2
- It is also recommended to avoid drinking a lot of alcohol over a short period of time.1
- If you drink alcohol, it is suggested to limit intake to 1 to 2 servings per day.2 Some examples of a serving include: 1 beer (12 ounces), 1 glass of wine (5 ounces), or 1 shot of liquor (1.5 ounces).1
- The amount you can safely drink also depends on body size and medical conditions.3 Consult with your pharmacist for more details.
Keep in mind that along with the items listed above, warfarin can also interact with medications, herbals and natural health products, vitamins, minerals, and more. Speak to your pharmacist for more information.
- Patient Education: Anti-clotting medicines: Warfarin (Coumadin) (The Basics). In: Post T, ed. UpToDate. Waltham, MA.: UpToDate; 2019. www.uptodate.com. Accessed February 13, 2019.
- Patient Education: Anti-clotting medicines: Warfarin (Coumadin) (Beyond the Basics). In: Post T, ed. UpToDate. Waltham, MA.: UpToDate; 2019. www.uptodate.com. Accessed February 13, 2019.
- Dietitians of Canada. Eating Guidelines for People Taking Warfarin Anticoagulants (Coumadin) [PDF File]. Health Stand Nutrition. Updated: April 16, 2009. Available at: