The study from the University of Guelph in Ontario, Canada used DNA bar-coding technology to test 44 herbal products sold by 12 companies.
Only two of the companies provided authentic products without substitutions, contaminants or fillers. Overall, nearly 60 percent of the herbal products contained plant species not listed on the label, researchers said.
Researchers detected product substitution in 32 percent of the samples. More than 20 percent 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.
"We found contamination in several products with plants that have known toxicity, side effects and/or negatively interact with other herbs, supplements and medications," said Newmaster.
One product labelled as St John's wort contained 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, researchers said.
Several herbal products contained Parthenium hysterophorus (feverfew), which can cause swelling and numbness in the mouth, oral ulcers and nausea. It also reacts with medications metabolised by the liver.
One ginkgo product was contaminated with Juglans nigra (black walnut), which could endanger people with nut allergies, the study involving research associate Subramanyam Ragupathy, U of G student Meghan Gruric and Sathishkumar Ramalingam of Bharathiar University in India, said.
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.
"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," said Newsmaster.
Regulatory problems involving natural health products continue to affect consistency and safety, Newmaster said.
"The industry suffers from unethical activities by some of the manufacturers," said Newmaster.

The study was published in the journal BMC Medicine.


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