Individuals with medical conditions that cause blood clots to form too easily are often prescribed warfarin, which also goes by the brand name Coumadin. This medicine reduces clot formation and lowers the risk of life-threatening blockages of blood flow to the heart or brain. Certain fruits, such as grapefruit, cranberries and avocado, contain chemical substances that may interfere with Coumadin function. Consult your healthcare professional before including these fruits in your diet while taking this drug.
Grapefruit and grapefruit juice contain chemical compounds that inhibit liver and intestinal enzymes responsible for metabolizing Coumadin. A case report published in the April 1999 issue of "American Journal of Health-System Pharmacy" showed that a 64-year old man taking Coumadin experienced increased blood-clotting speed after consuming 1 1/2 liters of grapefruit juice per day for two days, suggesting that the grapefruit juice interfered with Coumadin’s effects. However, another study published in the same journal showed that drinking 24 ounces of grapefruit juice per day for one week did not affect blood-clotting speed in a group of men taking Coumadin, suggesting that moderate consumption may not influence drug function. Nevertheless, check with your healthcare professional before consuming grapefruit and grapefruit juice.
Cranberries and cranberry juice may interfere with Coumadin’s effects, according to several case studies. For example, a 2011 publication in “The Annals of Pharmacotherapy” showed that a 46-year-old female who took Coumadin along with 1 1/2 quarts of cranberry juice cocktail per day for two days had a reduced blood-clotting speed compared to when she didn’t drink the juice, suggesting that cranberry juice accentuated the anti-clotting action of Coumadin. However, another study published in the “Journal of Clinical Pharmacology” indicated that drinking approximately 1 cup of cranberry juice per day for two weeks did not affect blood clotting in Coumadin users compared to those who drank a placebo drink. Although most of the cases showing a cranberry juice-Coumadin interaction involved consuming large volumes, check with your healthcare professional before regularly including any cranberries or cranberry products into your diet.
Avocados contain vitamin K, which is essential for the production of blood-clotting factors. Coumadin reduces blood-clot formation by inhibiting vitamin K activity and increasing the amount of time it takes to form a clot. So large fluctuations in your vitamin K intake influence this clotting time. Because the vitamin K content varies from 30 to 48 micrograms per cup of cubed avocado, according to the National Institute of Health Clinical Center, it’s hard to know how much vitamin K you’re consuming with each avocado serving. You may need to eliminate avocado from your diet if you’re taking Coumadin to avoid possible variations in vitamin K consumption.
The way Coumadin functions in your body is highly individual, and the interaction of certain fruits with the drug may be influenced by pre-existing health conditions. Additionally, the window of optimal therapeutic benefits is narrow for Coumadin, and drastic changes in your diet can influence this window. Ensure that your diet is relatively consistent, particularly your vitamin K intake, and consult your healthcare professional if you intend to make significant dietary changes.
- U.S. Pharmacist: Food and Lifestyle Interactions With Warfarin: A Review
- American Journal of Health-Systems Pharmacy: Grapefruit Juice and the Response to Warfarin
- Annals of Pharmacotherapy: Warfarin-Cranberry Juice Interaction
- Journal of Clinical Pharmacology: The Absence of an Interaction Between Warfarin and Cranberry Juice: a Randomized, Double-Blind Trial
- National Institutes of Health Clinical Center Drug-Nutrient Interaction Task Force: Warfarin (Coumadin) and Vitamin K
- Indiana Hemophilia and Thrombosis Center: Warfarin (Coumadin) Interactions with Food
- Johns Hopkins Health Alerts: Prescription Drugs on Grapefruit-Drug Interactions
- American Journal of Health-Systems Pharmacy: Grapefruit Juice Might Still be Factor in Warfarin Response