Drug-Herb Interactions with Coumadin


John Chen, Ph.D., Pharm.D., O.M.D., L.Ac

Warfarin (Coumadin) is commonly referred to as a blood thinner. It is frequently prescribed to prevent and treat stroke, heart attack, and others diseases characterized by obstruction of blood vessels with clots, leading to death of body tissues and/or organs. Warfarin (Coumadin) works by decreasing the synthesis of vitamin-K dependent clotting factors, which in turn interferes with the clotting process. Because warfarin (Coumadin) interferes with the clotting mechanism, it must be given and monitored carefully as overdose of the drug may lead to profuse bleeding and under-dose may lead to increased risk of thrombosis and embolism.

Patients who take warfarin (Coumadin) must be very careful when using other drugs, herbal medicines, and other supplements, as there are many factors which will interfere with its proper function; therefore, patients on warfarin (Coumadin) should not take any drugs, herbal medicines, or other supplements without first consulting a healthcare practitioner. Many prescription drugs, such as anti-inflammatory drugs, antibiotics, and anti-diabetic drugs may potentiate the effects of warfarin (Coumadin); while other drugs, such as anti-seizure, anti-fungal, and birth control drugs may diminish its effect.

Other than prescription drugs, there are western herbs and Chinese herbs that may also interfere with the proper function of warfarin (Coumadin). Western herbs such as garlic (Allium sativum), ginkgo (Ginkgo biloba), ginger (Zingiber officinale) and feverfew (Tanacetum parthenium) may potentiate the effect of warfarin (Coumadin); Chinese herbs that invigorate the blood circulation, such as Dan Shen (Radix et Rhizoma Salviae Miltiorrhizae), Dang Gui (Radix Angelicae Sinensis), Chuan Xiong (Rhizoma Chuanxiong), Tao Ren (Semen Persicae), Hong Hua (Flos Carthami), and Shui Zhi (Hirudo Whitmania), may also potentiate the effect of warfarin (Coumadin). On the other hand, herbs that stop bleeding, such as Pu Huang (Pollen Typhae), Xian He Cao (Herba Agrimoniae), Ce Bai Ye (Cacumen Platycladi), and Di Yu (Radix Sanguisorbae), may diminish the effect of warfarin (Coumadin).

Finally, other food and supplements, such as vitamin E, vitamin K, multi-vitamin complex, leafy green vegetables, and green tea may all interfere with proper function of warfarin (Coumadin).

In conclusion, proper caution is definitely needed for patients who take warfarin (Coumadin). Patients must understand the risks and the benefits of the drug, and should discuss everything with their healthcare practitioner – including drugs, herbal medicine, food, dietary supplements, and lifestyle. In addition, patients must have an open communication with their healthcare practitioners so that if adverse reactions occur, such as excessive bleeding or bruising, adjustment to the therapy can be made immediately. It is vital for medical doctors and pharmacists to understand what herbs and supplements are, and it is essential for herbalists to know what warfarin (Coumadin) is, and what it does. After all, optimal patient care can only be achieved when doctors communicate, and not condemn each other.

About the Author
Dr. John Chen is a recognized authority in both western pharmacology and Chinese Herbal Medicine, having combined formal training in both fields with extensive research 'on the ground' in China. He teaches at the USC School of Pharmacy, Emperor's College, Yo San University of TCM, OCOM, Five Branches, AOMA and ACTCM, and has taught numerous professional seminars across the U.S. and internationally. Dr. Chen's published works include Chinese Medical Herbology and Pharmacology (2003, AOM Press) and Chinese Herbal Formulas and Applications (2008, AOM Press) for which works he is the lead author.

To learn more about herb-drug interactions and herbal alternatives, click here to view a complete list of courses by John Chen.