Most store-bought bottles of Echinacea, ginkgo, St. John's wort and other popular herbal products are filled with unlisted ingredients, contaminants and fillers, found a new study, which quantified just how little consumers often know about products that are supposed to be good for them.
"Contamination and substitution in herbal products present considerable health risks for consumers," the researchers wrote in the journal BMC Medicine. "In our study, we found contamination in several products with plants that have known toxicity, side effects and/or negatively interact with other herbs, supplements, or medications."
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Herbal products generate billions of dollars of income for the companies that produce them, but recent media reports have highlighted the growing problem of false advertising and uncertain ingredients in all sorts of teas, nutraceuticals and medicinal plant supplements.
To investigate the extent of the problem, researchers from the University of Guelph in Canada analyzed the DNA of 44 herbal products made by a dozen companies. Most were capsules. A few were tablets or powders. All were easily accessible at supermarkets, health food stores, pharmacies or websites.
Nearly 60 percent of the samples contained plants that were not listed on the label, the study found. In more than 30 percent of products, there was not any sign of the plant that was supposed to be the main ingredient. And more than 20 percent contained fillers like rice, soybeans and wheat, which could unknowingly cause problems for people with allergies.
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Evidence of contamination raised yet more safety concerns. For example, a sample of St. John's wort, which is often taken for depression and anxiety, contained a plant that acts as a laxative and can cause chronic diarrhea and liver damage if taken over the long-term.
Several products contained feverfew, which can lead to swelling and numbness in the mouth. And a gingko sample contained black walnut, which is potentially dangerous for people with nut allergies.
For now, the herbal product market is a buyer-beware situation. But the new study used a technique called DNA barcoding, which might make it increasingly possible to catch companies in the act of selling herbal products that are something other than what they claim to be.