Interactions between herbal supplements and warfarin : a patient teaching tool

Abstract

Many Americans are using herbal supplements without telling their primary care providers. When a person is taking warfarin, a medication that has a narrow therapeutic window and the potential for interaction with many substances, including food, medications, and supplements, providers must inform them of the risks. A literature review was done to find current literature related to warfarin and herbal interactions. Limited quality data is available, with most literature found being case reports, and small population studies. A patient teaching pamphlet was created and tested using a pre-test/posttest in a convenience sample of 18 patients that use warfarin at an internal medicine clinic in Northern Wyoming. The results showed improvement in posttest scores in 17 of 18 participants. Mean improvement was 10.9%. Providers should include herbal supplements in routine medication history. Providers should teach all patients using warfarin about potential interactions with herbal supplements and about the need to inform their provider about supplements. Lack of standardization of herbal supplements makes it difficult to research the risks and benefits as well as potential interactions. More research is needed to determine risks.