Many people have a lot of faith in so-called "natural" health products and nutrition supplements, despite a lack of regulation and evidence that the substances are actually beneficial.
And now a study finds that of 44 herbal products tested, only two actually contained what they claimed to contain with no substitutes, contaminants or fillers.
The study, conoducted by researchers at the University of Guelph, wasÂ published recently in the open access journalÂ BMC Medicine. ItÂ used DNA barcoding technology to test 44 herbal products sold by 12 companies.
Overall, nearly 60 per cent of the herbal products contained plant species not listed on the label.Â Researchers detected product substitution in 32 per cent of the samples.Â More than 20 per cent of the products included fillers such as rice, soybeans and wheat not listed on the label.
"Contamination and substitution in herbal products present considerable health risks for consumers," said lead author Steven Newmaster, an integrative biology professor and botanical director of the Guelph-based Biodiversity Institute of Ontario (BIO), home of the Canadian Centre for DNA Barcoding.
"We found contamination in several products with plants that have known toxicity, side effects and/or negatively interact with other herbs, supplements and medications."
One product labelled as St. John's wort containedÂ Senna alexandrina, a plant with laxative properties. It's not intended for prolonged use, as it can cause chronic diarrhea and liver damage and negatively interacts with immune cells in the colon.
Several herbal products containedÂ Parthenium hysterophorusÂ (feverfew), which can cause swelling and numbness in the mouth, oral ulcers, and nausea. It also reacts with medications metabolized by the liver.
One ginkgo product was contaminated withÂ Juglans nigraÂ (black walnut), which could endanger people with nut allergies.
Unlabelled fillers such as wheat, soybeans and rice are also a concern for people with allergies or who are seeking gluten-free products, Newmaster said.
"It's common practice in natural products to use fillers such as these, which are mixed with the active ingredients. But a consumer has a right to see all of the plant species used in producing a natural product on the list of ingredients."
Until now, verifying what's inside capsules or tablets has posed challenges, Newmaster said. His research team developed standard methods and tests using DNA barcoding to identify and authenticate ingredients in herbal products.
"There is a need to protect consumers from the economic and health risks associated with herbal product fraud. Currently there are no standards for authentication of herbal products."
Medicinal herbs now constitute the fastest-growing segment of the North American alternative medicine market, with more than 29,000 herbal substances sold, he said.
More than 1,000 companies worldwide make medicinal plant products worth more than $60 billion a year.