A fifth of Indian herbal medicines sold on the internet contain potentially lethal substances, according to a new study in the United States.
The study at Boston university analysed 193 products and found that 20% of them contained lead, mercury or arsenic.
Herbal medicine has been used in India for thousands of years and is growing in popularity in the West.
The researchers said their findings showed that there should be stronger control of herbal supplements.
Writing in the Journal of the American Medical Association, lead researcher Dr Robert Saper said there was some evidence that herbs used in ayurvedic (Indian herbal) medicines could help against diabetes, high blood pressure and high cholesterol.
"But the key thing is we need to separate out what's helpful and.... what needs to be looked at and perhaps set aside," he added.
"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."
The researchers discovered the presence of toxic metals in ayurvedic medicines made both in India and the US.