Researchers from the University of Chicago report that ginseng interferes with warfarin, a drug commonly used to prevent blood clots. The researchers encourage anyone who takes both ginseng and warfarin, also known as Coumadin, to notify his or her doctor and urged doctors to ask patients on warfarin if they are taking ginseng.

“Warfarin has a narrow therapeutic index,” said study author Chun-Su Yuan, MD, “which means precise dosing is crucial.”

Yuan’s team studied 20 healthy volunteer subjects for four weeks. All subjects received 5 mg a day of warfarin for three days during week one and again in week four. Beginning in week two, 12 subjects took two grams of powdered ginseng in capsules. The other eight volunteers received a placebo. The researchers monitored blood levels of warfarin and the clotting ability of the blood.

They found that after two weeks, daily doses of ginseng significantly reduced the blood levels and the anti-clotting effects of warfarin.

Since ginseng alone can promote bleeding and delay clot formation, the researchers were surprised to find that it reduced the anti-clotting effect of warfarin compared to those who took the placebo. They suspect that substances within ginseng may enhance the function of enzymes that break down warfarin, clearing it from the blood stream more rapidly.

University of Chicago Medical Center, July 5, 2004