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Ginseng Dims Blood Thinner's Potency

Herb may undermine warfarin's anti-clotting action

WEDNESDAY, July 7, 2004 (HealthDayNews) -- For the estimated 3 million Americans taking the blood thinner warfarin, popping a ginseng supplement each day might not be such a good idea.

A small new study suggests ginseng speeds clearance of the drug from the liver, lowering its concentrations in the bloodstream and possibly raising a user's risk for heart attack or stroke.

"It's important that people on warfarin, if they are also taking ginseng, that they tell their physicians," said lead researcher Dr. Chun-Su Yuan, director of the Tang Center for Herbal Medicine Research at the University of Chicago. His team published their findings in the July 6 issue of the Annals of Internal Medicine.

As consumers take more direct control of their own health care, many seek out non-traditional, alternative therapies to maintain or improve their health. In fact, the market for herbals and other alternative remedies has boomed over the past few decades, with U.S. sales now reaching hundreds of millions of dollars per year.

At the same time, most of these products are placed on the market with little or no regulation and few scientific studies assessing either their safety or effectiveness.

Such was the case with ginseng. Although anecdotal reports of ginseng's negative effect on warfarin -- also known by the brand name Coumadin -- have been reported from time to time, Yuan said his team's study is one of the first controlled, clinical trials on ginseng ever conducted.

In the four-week study, the Chicago researchers had 20 healthy young volunteers take normal 5 milligram-per-day doses of warfarin for three days during week one, then again for another three days during week four.

Beginning in week two, 12 of the participants also began taking daily capsules containing 2 grams worth of powdered ginseng. The remaining eight volunteers took a placebo.

The researchers monitored blood concentrations of warfarin and any changes in the blood's clotting ability, over the study period.

"We observed that after two weeks of the ginseng administration in these normal subjects, the herb appeared to induce changes in warfarin [concentrations]," Yuan said. "Warfarin plasma concentrations and blood coagulation was reduced by ginseng."

These changes were "statistically significant," Yuan added. Changes in potency may be especially important when it comes to warfarin, since the drug has a very narrow "therapeutic index," or range within it which it produces its desired, protective effect on the cardiovascular system.

Indeed, the federally mandated package insert for warfarin states that "it cannot be emphasized too strongly that treatment of each patient is a highly individualized matter," and that patients on warfarin should be monitored over time to make sure the drug has its desired effect in reducing their risk for clots.

According to Yuan, ginseng probably affects the activity of specific liver enzymes, raising the rate at which the liver metabolizes warfarin and flushes it from the blood.

Steven Dentali, vice president of scientific and technical affairs at the American Herbal Products Association, which represents the industry, agreed with Yuan's advice.

"I think the message is clear -- that if you're going to be changing your diet or dietary supplements and you're on prescription medications, then you should talk to your doctor," he said.

Dentali pointed out that even common foods have been shown to effect significant changes in drug activity. Leafy green vegetables contain high doses of vitamin K, which can affect liver enzymes, he said, while grapefruit juice actually increases the absorption and activity of various drugs.

"The concept that botanicals or articles in the diet affect drug metabolism is not new," Dentali said. "We've certainly seen that with St. John's wort, which, in a similar fashion, can render some drugs less effective."

In fact, a review article of 20 different studies, published in the July 2 issue of The Lancet, found that St. John's wort reduced blood concentrations of a number of conventional drugs. In a prepared statement, the Canadian authors of that study said "higher quality research is necessary to provide reliable information to guide clinical practice."

Consumers of herbal products could benefit from better guidelines, too, according to Yuan. He pointed out that the "recommended dose" included on herbal labeling usually originates with the manufacturer, not an independent scientific source such as the FDA.

"In the herbal industry, dosing is very confused," he said. "Many consumers assume that herbals are natural, and natural equals safe. So you go to Walgreens or GNC and get these dietary supplements, and if you assume they're safe, you'll take high doses, thinking that if a little of this is good, then more is better."

Unfortunately, that's not always the case. "Herbs are pharmacologic agents," Yuan said. "They contain a lot of active ingredients."

More information

To learn more about dietary supplements like ginseng, head to the U.S. Food and Drug Administration.

SOURCES: Chun-Su Yuan, M.D., Ph.D., professor and director, Tang Center for Herbal Medicine Research, University of Chicago; Steven Dentali, Ph.D., vice president, scientific and technical Affairs, American Herbal Products Association, Delray Beach, Fla.; July 6, 2004, Annals of Internal Medicine; July 2, 2004, The Lancet
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