Levels of lead, mercury and arsenic that exceed "acceptable standards" can often be found in traditional Indian remedies sold on the internet, a study has found.
Researchers who analysed 193 randomly selected Ayurvedic medicine products bought online found that a fifth contained worrying concentrations of the toxic metals.
The highest levels of lead and mercury were found in medicines made by the ancient practice of rasa shastra, which deliberately combines herbs with metals, minerals and gems.
Several of these Indian-manufactured remedies could result in people consuming doses of lead and mercury 100 to 10,000 times greater than acceptable limits, according to experts.
Ayurveda is a form of traditional medicine and health philosophy that originated in India more than 2,000 years ago and relies heavily on herbal products.
Rasa shastra experts maintain that if these medicines are properly prepared and administered they are safe and effective.
The research, the findings of which have been published in the Journal of the American Medical Association, involved randomly buying Ayurvedic medicines from the internet and analysing them in a laboratory.
Team leader Dr Robert Saper, from Boston University School of Medicine in Massachusetts, US, said: "Our first priority must be the safety of the public.
"Herbs and supplements with high levels of lead, mercury and arsenic should not be available for sale on the internet or elsewhere."