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By Richard Sadovsky, M.D.

Although herbal preparations may be useful for some disorders, safety evaluations are limited. Because certain prescribed medications have a narrow therapeutic window, interactions with herbs need to be assessed. American ginseng, one of the most popular herbs in the United States, is believed to maintain good health, fight fatigue, and boost immune function. However, it also has been noted to promote bleeding in surgical patients, and is reported to reduce the efficacy of warfarin. Yuan and associates carried out a randomized, double-blind, placebo-controlled trial using 20 young, healthy volunteers to clarify the potential interaction between ginseng and warfarin.

Participants were given a 5-mg dose of warfarin on each of the first three days of the study, then in the second week were assigned randomly to oral American ginseng (1 g twice per day)or placebo for three weeks. On the first three days of week 4, participants again were given warfarin. All participants were instructed to maintain a diet consistent in vitamin K.

A small but significant reduction in the International Normalized Ratio (INR) was noted in the ginseng group from weeks 1 to 4 compared with the change in the placebo group. The average daily vitamin K intake, measured by diet diaries, did not differ significantly between the two groups.

The authors conclude that American ginseng reduced the anticoagulant effect of warfarin by induction of hepatic P450 enzyme system activity and increased warfarin elimination. Because the INR reduction was statistically significant after ginseng intake for two weeks, it is likely that more than one week of ginseng intake is necessary to induce this metabolic pathway.

Yuan CS, et al. American ginseng reduces warfarin's effect in healthy patients. Ann Intern Med July 6,2004;141:23-7.

EDITOR 'S NOTE: Because use of herbal medications is so prevalent, physicians need to help their patients understand some of the potential safety issues. Just because these preparations can be purchased without a prescription does not mean that they are risk free. A review of ginkgo biloba points out that it inhibits the platelet-activating factor, making use of this herb with warfarin, aspirin, or any other antiplatelet medication potentially dangerous. (1) Ginkgo intake should be stopped before a patient undergoes any procedure that might result in significant bleeding. Other herbs taken with ginkgo, such as garlic, feverfew, or ginseng, can increase the bleeding risk. (1) Hypersensitivity to ginkgo is rare, as are side effects, though mild nausea, vomiting, diarrhea, headaches, dizziness, and palpitations have been reported. Physicians should try to recommend treatments that are known to be safe and effective, but also should support patients who want to try herbal preparations safely for reasonable purposes, and help them monitor their progress with the treatment. (2) The American Botanical Council, a nonprofit research and educational association, offers information about herbal preparations on their Web site, at:http://www.herbalgram.org.--R.S.


(1.) Sierpina VS, Wollschlaeger B, Blumenthal M. Ginkgo biloba. Am Fam Physician 2003;68:923-6.

(2.) Zink T, Chaffin J. Herbal "health "products: what family physicians need to know. Am Fam Physician 1998;58:1133-40.

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