Because herbal medicines are considered dietary supplements, their manufacturers don't have to prove that they are either safe or effective in order to market them in the United States. Researchers at Harvard and the Environmental Protection Agency tested ayurvedic medicines for heavy metals.

What the researchers wanted to know: How common are lead, mercury, arsenic, tin, silver, gold, and cadmium in ayurvedic herbal medicines?

What they did: The researchers used www.superpages.com's online yellow pages to find stores in and near Boston that sold ayurvedic (traditional Indian) herbal remedies. They bought one of every medicine they could find—70 different products—and sent them to the EPA's regional lab to be analyzed for heavy metals. For each one that turned up lead, mercury, or arsenic, they went back to the store to buy another one to re-test; most were still available, and those that were retested had levels similar to the first test.

What they found: Fourteen of the 70 products contained lead, mercury, and/or arsenic. Seven of those products were recommended for children; for example, 21 of the 30 stores sold a product called Safi, recommended for children, which contained 54 micrograms of arsenic per milliliter. If a child took that medicine daily in the recommended doses, he could get more than 10 times what the EPA calls the "reference dose" of arsenic—a dose of a toxin near the upper limit of safety. Some products could expose adults or children to thousands of times the reference dose of lead, mercury, or arsenic. Some products had high levels of all three.

What the study means to you: Just because it's herbal doesn't mean it's safe. According to ayurvedic theory, certain metals are supposed to help cure you, but there have been cases of heavy metal poisoning from some ayurvedic medicines.

Caveats: The researchers didn't know what chemical form the metals were in, which can affect how toxic they are.

Find out more: The EPA explains the reference dose at www.epa.gov. Scroll down to 1.3.2.3 Reference Dose (RfD).

Read the article: Saper, R.B., et al. "Heavy Metal Content of Ayurvedic Herbal Medicine Products." Journal of the American Medical Association. Dec. 15, 2004, Vol. 292, No. 23, pp. 2868-2873.

Abstract online: http://jama.ama-assn.org