Herbs & Dietary Supplements Database : Herbs & Supplements that Interact with Blood Thinners

Dr. James Manos (MD)
July 5, 2019

Herbs, dietary supplements, and foods that may interact with blood thinners such as warfarin (Coumadin®)

Warfarin (Coumadin®) is a medicine prescribed for people at increased risk of forming blood clots. Sometimes medical conditions can make blood clot too easily and quickly. This could cause serious health problems because clots block blood flow to the heart or brain. Warfarin can prevent harmful blood clots from forming. Blood clots are created through a series of chemical reactions in the body. Vitamin K is essential for those reactions. Warfarin works by decreasing the activity of vitamin K, lengthening the time it takes for a clot to form. International Normalized Ratio (INR) and Prothrombin Time (PT) are laboratory test values obtained from measurements of the time it takes blood to clot. Individuals at risk for developing blood clots take warfarin to lengthen the usual time for a clot to form, resulting in a prolonged INR/PT. Doctors measure the INR/PT every month in patients taking warfarin to ensure it stays in the desired range (6).

Herbal products that may potentially increase the risk of bleeding or potentiate the effects of warfarin therapy include angelica root, arnica flower, anise, asafetida, bogbean, borage seed oil, bromelain, capsicum, celery, chamomile, clove, fenugreek, feverfew, garlic, ginger ginkgo, horse chestnut, licorice root, lovage root, meadowsweet, onion, parsley, passionflower herb, poplar, quassia, red clover, rue, sweet clover, turmeric (curcumin), and willow bark (1).

Products that have been associated with documented reports of potential interactions with warfarin include coenzyme Q10, danshen, devil's claw, dong quai, ginseng, green tea, papain, and vitamin E. Interpretation of the available information on herb-warfarin interactions is difficult because nearly all of it is based on in vitro data, animal studies, or individual case reports. More studies are needed to confirm and assess the clinical significance of these potential interactions. There is evidence that a wide range of alternative therapy products has the potential to interact with warfarin (1).

Cranberry, Dong Quai (Angelica sinensis), garlic, glucosamine +_ chondroitin, papaya extract, Tan–Shen (Danshen), and vitamin E may increase the effect of warfarin (papaya extracts’ impact is less than the rest mentioned above) (2).

Panax ginseng and St. John’s Wort may decrease the effect of warfarin (ginseng’s effect is less than St. John’s Wort) (2).

Evidence suggests that vitamin E has blood-thinning effects. Vitamin E intake above 1,000 International Units (IU) per day may increase the risk of excess bleeding. Research suggests that doses up to 800 IU may be safe for individuals on warfarin (Coumadin®), but the evidence is inconclusive. It is best for someone to ask a physician about taking Vitamin E supplements while taking warfarin (6).

Some herbs that may interact with warfarin include feverfew, garlic, ginger, ginkgo, ginseng, bilberry, dong quai, turmeric (curcumin), meadowsweet and willow, chamomile, motherwort, horse chestnut, fenugreek, and red clover. Omega 3 fatty acids (oils) may also interact with warfarin (3).

Warfarin may interact with many Chinese herbs (4).

Note: for a list of Chinese herbs that may interact with warfarin, see Reference (4).

Herbs & dietary supplements that may interact with warfarin include: chondroitin plus glucosamine, coenzyme Q10 (also known as ubiquinone, ubidecarenone), danshen (Salvia miltiorrhiza), devil’s claw (Harpagophytum procumbens), dong quai (also known as danggui), Chinese angelica (Angelica sinensis), feverfew (Tanacetum parthenium), fenugreek together with boldo (Peumus boldus), fish oil supplements that contain eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), Ginkgo biloba, ginseng (Panax ginseng), Chinese ginseng, Japanese ginseng, Korean ginseng, American ginseng (Panax quinquefolius), green tea (Camellia sinensis), horse chestnut (Aesculus hippocastanum), Lycium barbarum(also known as Chinese wolfberry, Di GU Pi, Goji berry, Gou Qi Li), papaya extract (containing papain), specific brands of quilinggao (also known as΄΄essence of tortoise shell΄΄), St. John's Wort (Hypericum perforatum), vitamin A, vitamin K, and wintergreen (used on the skin, also known as methyl salicylate) (5).

Many herbs & dietary supplements may interact with warfarin. They can alter the INR/PT, such as arnica, bilberry, butcher's broom, cat’s claw, dong quai, feverfew, forskolin, garlic, ginger, ginkgo, horse chestnut, inositol hexaphosphate, licorice, melilot (sweet clover), pau d’arco, red clover, St. John’s wort, sweet woodruff, turmeric, willow bark, and wheatgrass. Much is unknown about dietary supplements. The safest policy is for individuals on warfarin to avoid all dietary supplements unless their doctor approves. This includes any vitamin/mineral supplements that list vitamin K on the label. If they are taken regularly on a daily basis, they pose less of a problem than if taken off and on (6).

People taking warfarin should keep their intake of foods rich in vitamin K about the same each day. For example, someone may plan to eat only half a cup of these foods daily. If someone likes these foods and eats them often, he/she can eat more, but be consistent. People on warfarin should not significantly change their intake of foods rich in vitamin K. For example, if someone typically has a spinach salad daily, he/she should not stop eating it entirely (6).

Note: for a list of foods and the amount of vitamin K they contain, see Reference (6).

Foods that affect warfarin or blood clotting include avocado, cranberry juice, flax (flaxseed), garlic, ginger, mango, onions, papaya, seaweed (sushi wrap), and soy protein products (including soy milk and tofu) (5).

While eating insignificant amounts of foods rich in vitamin K shouldn't cause a problem, patients taking warfarin should avoid eating or drinking substantial amounts of kale, spinach, Brussels sprouts, parsley, collard greens, mustard greens, chard, and green tea (7).

Alcohol can affect warfarin dose and should be avoided (6).

Certain drinks can increase the effect of warfarin, leading to bleeding problems. People taking warfarin should avoid or drink only small amounts of these drinks when taking warfarin: cranberry juice and alcohol (7).

Thanks for reading!

Reference - Links:

1. http://www.ncbi.nlm.nih.gov/pubmed/10902065