Dietary supplement-drug interactions.

Recent surveys show that 18% of adults in the United States use prescription drugs concurrently with herbal or vitamin products, placing an estimated 15 million patients at risk of potential drug-supplement interactions. Despite this widespread concurrent use of conventional and alternative medicines, documented drug-herb interactions are sparse. This review focuses on possible interactions between drugs and herbal medicines used for phytoestrogen-hormone and antiplatelet-oral anticoagulant therapy. Interactions with phytoestrogens are purely speculative, based on competitive estrogen-receptor binding or antiestrogenic effects. In contrast, several case reports document bleeding complications with Ginkgo biloba, with or without concomitant drug therapy. Case reports are also suggestive of interaction between warfarin and dong quai or Panax ginseng. Recommendations for counseling patients at highest risk of adverse interactions are given.