From the Guidelines
Foods high in vitamin K, such as green leafy vegetables, can significantly affect warfarin's effectiveness by reducing its blood-thinning action, and patients should maintain a consistent intake of these foods to avoid destabilizing INR levels. The most recent and highest quality study on this topic, published in 2022 1, highlights the importance of consistency in diet for patients taking warfarin. Key foods that can interact with warfarin include:
- Green leafy vegetables like kale, spinach, collard greens, and Brussels sprouts, which are high in vitamin K
- Cranberry juice and grapefruit juice, which can increase warfarin's effects and potentially lead to dangerous bleeding
- Herbal supplements such as St. John's wort, which can enhance clearance of warfarin and reduce INR levels
- Other fruits like pomegranate, avocado, mango, and papaya, which may interact with warfarin, although the evidence is limited
It is essential for patients taking warfarin to discuss any significant dietary changes with their healthcare provider, who may need to adjust the warfarin dosage accordingly. Regular INR monitoring is also crucial when making dietary modifications while on warfarin therapy, as noted in a previous study 1. By maintaining a consistent diet and monitoring INR levels, patients can minimize the risk of adverse interactions between warfarin and certain foods.
From the FDA Drug Label
Specific botanicals reported to affect warfarin sodium tablets therapy include the following: Bromelains, danshen, dong quai (Angelica sinensis), garlic, Ginkgo biloba, ginseng, and cranberry products are associated most often with an INCREASE in the effects of warfarin sodium tablets. Coenzyme Q10 (ubidecarenone) and St John’s wort are associated most often with a DECREASE in the effects of warfarin sodium tablets.
The foods that affect warfarin the most are those that contain vitamin K, as they can decrease the effects of warfarin. However, the provided drug labels do not specify which foods have the most significant impact.
- Foods that may increase the effects of warfarin include those with anticoagulant, antiplatelet, and/or fibrinolytic properties, such as:
- Garlic
- Ginkgo biloba
- Ginseng
- Cranberry products
- Foods that may decrease the effects of warfarin include those with coagulant properties, such as:
From the Research
Foods that Affect Warfarin
Foods that affect warfarin the most are those high in vitamin K, as it can interact with warfarin and alter its anticoagulant effect.
- Dark, green vegetables are primary sources of dietary vitamin K 3
- Certain plant oils and prepared foods containing these plant oils, such as baked goods, margarines, and salad dressings, are also sources of dietary vitamin K 3
- A constant dietary intake of vitamin K that meets current dietary recommendations of 65-80 micrograms/day is recommended for patients on warfarin therapy 3
Mechanism of Interaction
The interaction between warfarin and vitamin K is due to the mechanism of action of warfarin, which is a vitamin K antagonist 4.
- Fluctuations in dietary vitamin K intake can have a significant effect on the degree of anticoagulation in patients treated with warfarin 5
- Sudden changes in eating patterns can significantly alter anticoagulation control, potentially exposing patients to the risk of bleeding or thromboembolic complications 4
Management of Interaction
To minimize the interaction between warfarin and foods, patients should be aware of the sources of vitamin K and their potential effect on anticoagulation response to warfarin 4.
- A stable dietary vitamin K, promoted by daily oral vitamin K supplementation, can improve anticoagulation stability in patients on warfarin therapy 4
- Low-dose oral vitamin K supplementation may be beneficial for patients with a variable response to warfarin, but larger, higher quality trials are needed to confirm this 6