"We wish to alert the medical community to a substantial threat to well-being posed by a particular form of herbal remedy, namely, Ayurvedic medicine," doctors said in a report in the latest New Zealand Medical Journal.
The eight patients suffered a range of symptoms, including abdominal pain, after taking Ayurvedic powders or tablets, one of which was claimed to be a treatment for male infertility.
One tablet contained 10 mg of lead, with a recommended dose of four a day.
The doctors said that under guidelines set by the UN Food and Health Organisation, a 70 kg adult, taking a single tablet containing 8 mg of lead, would get four times the tolerable weekly intake of lead.
They said that traditional Ayurvedic medicines containing lead or mercury are therapeutically beneficial, but added, "This belief is irreconcilable with Western toxicology".
"From the view of Western science, even minuscule quantities of lead have potential for harm, including irreversible brain damage, and are of absolutely no therapeutic benefit."
The doctors cited US research showing that 20 percent of Ayurvedic preparations bought in Boston contained substantial amounts of heavy metals.