American ginseng reduces warfarin's effect in healthy patients: a randomized, controlled trial

Abstract

Background People using prescription medication often concurrently take herbal supplements. In a case report, the anticoagulant effect of warfarin decreased after patients consumed ginseng. Objective To evaluate the interactions between American ginseng and warfarin. Design Randomized, double-blind, placebo-controlled trial. Setting General Clinical Research Center, University of Chicago, Chicago, Illinois. Participants 20 healthy patients. Intervention In 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. Measurements International normalized ratio (INR) and plasma warfarin level. Results The 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. Limitations The study sample consisted of young, healthy volunteers in a research setting rather than patients taking therapeutic doses of warfarin. Conclusions American ginseng reduces warfarin's anticoagulant effect. When prescribing warfarin, physicians should ask patients about ginseng use.