A new study shows that many herbal products do not contain the listed plant ingredients and instead have fillers or other cheaper chemicals.

The study, conducted by researchers at the University of Guelph, found that only two of the 12 companies studied had products with authentic plant derivatives. Researchers also found that about 60 percent of the natural products had plant species that weren't listed on the label.

And, around 32 percent supplements had cheaper substitutes added to them and over 20 percent had other fillers such as rice or wheat.

For the study, researchers used DNA barcoding technology to test 44 herbal products marketed by 12 companies.

"Contamination and substitution in herbal products present considerable health risks for consumers," said Steven Newmaster from the University of Guelph and lead author of the study.  "We found contamination in several products with plants that have known toxicity, side effects and/or negatively interact with other herbs, supplements and medications."

Taking some of these so-called herbal remedies could actually cause health damage.  St. John's wort- one of the products included in the study had Senna alexandrina, a plant known for its laxative properties. Long term exposure to this plant could cause diarrhea and even liver disease.

Many products included in the study had Parthenium hysterophorus (feverfew), which can cause numbness of mouth and oral ulcer.

People with any kind of allergy could be better off by staying away from these herbal medicines. The study found that at least one company selling a ginko product had mixed Juglans nigra, which is a black walnut and could trigger a reaction in people who are allergic to nuts.

Then, there are products that have wheat, which could harm people with gluten allergy.

"It's common practice in natural products to use fillers such as these, which are mixed with the active ingredients. But a consumer has a right to see all of the plant species used in producing a natural product on the list of ingredients."

About 80 percent of people in developed countries use herbal supplements, even though there is significant doubt about the authenticity of many ingredients used in them. A recent report by the Greenpeace East Asia called 'Chinese Herbs: Elixir of Health or Pesticides Cocktail?,' has shown the prevalence of pesticides in these products. The market value of traditional Chinese herbal products around the world is around US$ 60 billion.

The study is published in the journal BMC Medicine.