Ginseng reduces effects of anti-clotting drug

July 5, 2004

Researchers from the University of Chicago report in the July 6, 2004, issue of the Annals of Internal Medicine that ginseng, one of the best selling herbal supplements in the United States, 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, PhD, "which means precise dosing is crucial."

"With too small a dose," added Yuan, the Cyrus Tang Professor of Anesthesia & Critical Care and director of the Tang Center for Herbal Medicine Research at the University of Chicago, "the risk of clots increases, but too much can cause serious bleeding. So a substance, such as ginseng, that alters warfarin's effects, even slightly, can have significant consequences."

The 'blood-thinner' warfarin, taken once a day by about 3 million people in the U.S., is used to prevent blood clots from forming or growing larger. It is often prescribed for patients with certain types of irregular heartbeat, those who have had a heart attack or undergone heart valve replacement surgery. It prevents the formation of substances that cause clots.

Package inserts stress the importance of maintaining the proper dose. "It cannot be emphasized too strongly," notes the insert, "that treatment of each patient is a highly individualized matter. Warfarin sodium, a narrow therapeutic range drug, may be affected by factors such as other drugs and dietary Vitamin K. Dosage should be controlled by periodic determinations of prothrombin time," a measure of clotting speed.

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.

The National Institutes of Health and the Tang Center for Herbal Medicine Research funded this study. Additional authors include Gang Wei, Lucy Dey, Theodore Karrison, Linda Nahlik, Spring Maleckar, Kristen Kasza, Michael Ang-Lee, and Jonathan Moss of the University of Chicago.