Natural Medicines Newsletter

Volume 1, Issue 38, 10/08/2009

Question

What are some commonly used herbal or natural medicines that interact with warfarin (Coumadin®; Jantoven®) and cause changes in the INR?

Answer

Warfarin (Coumadin®; Jantoven®) is an oral anticoagulant most commonly used for the prevention and treatment of thromboembolic events (blood clots) in patients with atrial fibrillation, prosthetic heart valves, venous thrombosis and/or pulmonary embolism.(1)  Due to the availability of herbal or natural medicines without a prescription and the ability of patients to use them without the knowledge of their healthcare providers, it is plausible that patients on warfarin could self medicate with these products thereby causing a change in both the efficacy and safety of warfarin.  Their use together have been described in numerous case reports in the medical literature.  The likelihood for herb-drug interactions is expected to increase secondary to expanding use of herbal and natural medicines among people in the United States and around the world.(2) Therefore, the prudent clinician should be able to recognize the common herbal or natural medicines that interact with warfarin and thereby cause changes in the international normalized ratio (INR). 

The table below provides a concise summary of some of the more common herbal and natural medicines used by patients that are known to influence the efficacy and safety of warfarin.(3-34)  While the majority of herbal products are known to increase...  

The complete answer to this question comes with a table that summarizes the common herbs known to interact with warfarin and the proposed mechanisms for the interaction. 

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