Researchers at the University of Guelph used DNA barcode testing to test 44 herbal products from 12 companies. DNA barcoding uses a short sequence of DNA from a standard segment in plants to identify the species rapidly and accurately.

"Product substitution occurred in 20/44 of the products tested and only 2/12 companies had products without any substitution, contamination or fillers," Steven Newmaster, an integrative biology professor at the University of Guelph and his co-authors concluded in Friday's issue of the journal BMC Medicine.

"Some of the contaminants we found pose serious health risks to consumers."