DNA barcoding reveals herbal pill contamination

Got a cold? Take some Echinacea. Tired? Pop a ginseng. Americans spend billions of dollars on herbal supplements every year, but beware – they are not all what they seem.

A study has revealed that almost 60 per cent of common herbal supplements sold in the US and Canada contained products not listed on the label, some of which could pose serious health risks to consumers.

Steven Newmaster at the University of Guelph in Ontario, Canada, and his colleagues used a sequencing technique called DNA barcoding to identify plant material in 44 herbal products from 12 companies. He compared those to leaf samples of known provenance. In 32 per cent of the samples containing unlisted plant species, the main plant had been replaced with something else. Some also contained unlabelled fillers such as grass, wheat or rice.

Several samples contained contaminants with known side effects or which interact negatively with other medicines, and could present considerable health risk to consumers. For example, a sample labelled as St John's Wort was actually substituted with extract of the plant Senna alexandrina. This is an FDA approved herbal laxative, and is not recommended for prolonged use as it can cause side effects such as chronic diarrhoea and liver damage.

Other products were contaminated with Parthenium hysterophorus, a type of plant commonly known as feverfew, which has side effects including numbness of the mouth and nausea, and can heighten the risk of bleeding when taken with blood-thinning medicines such as Warfarin.