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June 1, 2000 (Washington) -- A class of Asian herbs used by dieters has been linked to kidney failure or cancer, the FDA warns in a "Dear Doctor" letter. The agency says these botanical products are included in the Aristolochia species and will be the subject of "appropriate regulatory actions" in the near future.

Those who prescribe botanical remedies are being urged by the FDA to discard products that contain these suspect ingredients. The reason is that Aristolochia botanicals contain aristolochic acid, a chemical that causes kidney damage and even kidney failure, according to reports in the medical literature. Some patients have required dialysis or even kidney transplants as a result of using the substances.

The FDA says that so far there are no such injury reports in the U.S. However, given the growing popularity of dietary supplements and botanical remedies, physicians are being advised to ask their patients if they've taken these preparations, particularly in cases of unexplained kidney problems.

Last year, the FDA says two new cases of severe kidney disease linked to Chinese herbs were reported in the U.K. One of the individuals has received a transplant; the other is awaiting the operation.

During the early 90s, more than 100 Belgian patients were prescribed a Chinese diet pill that contained, among other substances, aristolochic acid, which was mistakenly used in place of another substance that has a similar Chinese name, according to the FDA letter. So far, 70 of these patients have required a kidney transplant or dialysis.

Potentially even more frightening is that this potent group of herbs has caused cancer in animals, including tumors of the kidney, bladder, stomach, and lung. Also, cancers of the urinary tract have been diagnosed in some patients who have taken these supplements.

"Based on these studies, patients taking aristolochic acid may be at increased risk of developing cancers," says the FDA letter.

A scientist specializing in plant-derived medications agrees that botanicals containing aristolochic acid are toxic in high doses. However, Restem Medora, PhD, of the University of Montana, tells WebMD that these herbs are often taken in small amounts by people in South America and India for a variety of ailments.

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