• Chun-Su Yuan, Gang Wei, Lucy Dey, Theodore Karrison, Linda Nahlik, Spring Maleckar, Kristen Kasza, Michael Ang-Lee, and Jonathan Moss.
• Tang Center for Herbal Medicine Research, Committee on Clinical Pharmacology and Pharmacogenomics, Anticoagulation Consult Service, Pritzker School of Medicine, The University of Chicago, Chicago, Illinois 60637, USA. cyuan@uchicago.edu
• Ann. Intern. Med. 2004 Jul 6; 141 (1): 232723-7.

BackgroundPeople using prescription medication often concurrently take herbal supplements. In a case report, the anticoagulant effect of warfarin decreased after patients consumed ginseng.ObjectiveTo evaluate the interactions between American ginseng and warfarin.DesignRandomized, double-blind, placebo-controlled trial.SettingGeneral Clinical Research Center, University of Chicago, Chicago, Illinois.Participants20 healthy patients.InterventionIn this 4-week study, 20 patients received warfarin for 3 days during weeks 1 and 4. Beginning in week 2, patients were assigned to receive either American ginseng or placebo.MeasurementsInternational normalized ratio (INR) and plasma warfarin level.ResultsThe peak INR statistically significantly decreased after 2 weeks of ginseng administration compared with placebo (difference between ginseng and placebo, -0.19 [95% CI, -0.36 to -0.07]; P = 0.0012). The INR area under the curve (AUC), peak plasma warfarin level, and warfarin AUC were also statistically significantly reduced in the ginseng group as compared with the placebo group. Peak INR and peak plasma warfarin level were positively correlated.LimitationsThe study sample consisted of young, healthy volunteers in a research setting rather than patients taking therapeutic doses of warfarin.ConclusionsAmerican ginseng reduces warfarin's anticoagulant effect. When prescribing warfarin, physicians should ask patients about ginseng use.

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