American Ginseng Affects Prescription Blood Thinners

CHICAGO--Previous studies have linked intake of some herbal products with reduced efficacy of certain pharmaceuticals. The most recent example was published in the Annals of Internal Medicine (141, 1:23-7, 2004) (www.annals.org), in which researchers linked intake of American ginseng with reduced efficacy of the prescription anticoagulant warfarin.

Conducted at the University of Chicago, the study involved 20 healthy volunteers who received warfarin for three days during the first and fourth week of the month-long study, plus American ginseng or placebo beginning in the second week. Researchers found ginseng intake significantly reduced peak plasma warfarin levels and the drug's anticoagulant effect.

In a related Patient Summary (141, 1:I-58, 2004), the Annals editors suggest doctors ask their patients about ginseng use, and note larger doses of warfarin may be necessary to achieve the desired effects on blood clotting in patients taking ginseng.