Research News

Herbal products are often contaminated, study finds

BMJ 2013; 347 doi: (Published 11 October 2013) Cite this as: BMJ 2013;347:f6138
  1. Jacqui Wise
  1. 1London

Herbal medicines are frequently contaminated or contain plant species that are a substitute for the plants listed on the label or contain other species that may be a filler, a DNA analysis has found.

Some of the herbal medicines analysed were contaminated with plants that have known toxicity or can interact with other supplements or medications, the study reported in the open access journal BMC Medicine found.

Researchers from the Biodiversity Institute of Ontario in Canada used DNA barcoding to blind test 44 herbal products from 12 companies. They found that 59% of the products tested contained DNA barcodes from plant species not listed on the labels.1

Two thirds of the products tested had plant species present that were a substitute for the plants listed on the label. The researchers also found that a third of the products contained other species that may be a filler or contamination. These fillers included rice, soybean, and various grasses such as wheat.

Some of the unlabelled ingredients could pose a serious health risk. For example, one product labelled as St John’s wort (Hypericum perforatum) actually contained Senna alexandrina, which is a herbal laxative and not for prolonged use as it can cause cathartic colon and liver damage.

The researchers also found several products contaminated with feverfew (Parthenium hysterophorus), which can cause a number of side effects such as vomiting and abdominal pain. It should not be consumed by pregnant women and can interact with a variety of medications metabolised by the liver. It may also increase the risk of bleeding, especially if taken with blood thinning medications such as warfarin or aspirin. Feverfew is an invasive weed and it is likely that it was harvested along with the crop used to make the herbal product.

The study’s lead author, Steven Newmaster, of the University of Guelph in Ontario, called on the herbal industry to use DNA barcoding to authenticate herbal products and boost consumer confidence.


Cite this as: BMJ 2013;347:f6138