In the new study, published in today's issue of the Annals of Internal Medicine, Chun-Su Yuan, director of the Tang Center for Herbal Medicine Research at the University of Chicago, said he gave 20 healthy subjects 5 mg of warfarin daily for three days during week one and again in three weeks later.
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.
"Warfarin has a narrow therapeutic index," said Yuan, "which means precise dosing is crucial."
"With too small a dose, 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," he added.
Warfarin 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 is the most common oral anticoagulation therapy and its use is growing.
As NutraIngredientsusa.com reported last month, the issue of labelling herbals so that the public and health care officials have all possible information at their fingertips is a widely discussed topic in the US.
Last year the American Botanical Council (ABC) teamed up with Pharamvite, makers of Nature's Resource herbs, to launch the safety labeling program (SLP). This was designed to provide "quality, science-based safety information on specific herbs to manufacturers to provide the basis for warnings and directions on their product labels."
However, only Pharamvite and a handful of other manufacturers have signed up to the SLP. The reason for this may be financial, as the scheme probably adds 80 cents to $1 to the cost of a bottle of supplements.
But all herbal manufacturers may find that clear labelling and further rearch are necessary to minimise the risk of liability. The precedent was set last month when a woman who suffered brain damage in a stroke after taking the now banned dietary supplement ephedra received a $7.4 million jury award.