(United Press International via COMTEX) -- University of Chicago researchers report the popular herbal supplement ginseng can interfere with a common drug used to prevent blood clots.

Warfarin -- also known as Coumadin -- is used by nearly 3 million Americans with heart conditions to keep blood clots from forming. The study said its therapeutic effects have a very narrow range, so the precise dosage is crucial.

"With too small a dose, the risk of clots increases, but too much can cause serious bleeding," Dr. Chun-Su Yuan, director of the university's herbal medicine research center, said in a statement. "So a substance, such as ginseng, that alters warfarin's effects, even slightly, can have significant consequences."

The researchers studied 20 healthy subjects for four weeks and compared the effects of ginseng and a placebo on the functioning of warfarin, finding ginseng significantly reduced the drug's anti-clotting effects.

Ginseng itself is capable of causing bleeding and delaying clot formation, so researchers said they were surprised that it inhibited warfarin's effects, rather than enhancing them.

From Healthy.net