This is from U of Guelph

Very interesting...

http://www.uoguelph.ca/news/2013/10/study_herbal_pr.html
and from the interview
http://www.nytimes.com/2013/11/05/science/herbal-supplements-are-often-not-what-they-seem.html?_r=2 &

The study, published in the journal BMC Medicine, used DNA barcoding 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 per cent of the herbal products contained plant species not listed on the label.

More than 20 per cent of the products included fillers such as rice, soybeans and wheat not listed on the label.

“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 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.