The executive agency of the department of health's advice that consumers avoid taking six brands of ayurvedic herbal products follows a similar warning issued by Health Canada last month.
Traditional Ayurvedic medicines, which have been used in India for around 2000 years, may contain herbal ingredients that are processed using heavy metals such as mercury, lead and arsenic. While small amounts cause no ill effect and according to the Ayurvedic tradition may possess therapeutic properties, at high levels they can be toxic.
"Medicinal products containing high levels of heavy metals pose a serious public health risk," said MHRA director of executive support Roy Alder.
Heavy metals can accumulate in the vital organs, and children are the most at risk from their toxic effects.
"Many of the products we suspect to have entered the UK may contain mercury, arsenic and lead," added Alder.
Symptoms of arsenic poisoning are listed as nausea, abdominal pain, vomiting, muscle cramps, heart abnormalities, liver damage, anaemia and reduced motor nerve function.
Lead poisoning can cause weight loss, insomnia, dizziness, swelling of the brain and paralysis, and Mercury poisoning can cause tremors, insomnia, memory loss, slowed sensory and motor nerve function, and reduced mental function.
The products MHRA is advising UK consumers to avoid are: Karela tables (made by Shriji Herbal Products); Karela capsules (Himalaya Drug Co); Yograi Guggal and Sudarshan tablets (both Zandu Pharmaceuticals); Shilajit capsules (Darbur India); SAFI liquid (Hamdard-WAKF); and Maha Sudarshan Churna Powder (supplied by Zandu Pharmaceuticals, D&K Pharmacy, Chhatrisha and Dabur India).
MHRA has not ascertained that the products are definitely on the market in the UK, but says that it is "actively surveying the UK market" in collaboration with representatives of practitioners, manufacturers and retailers of Ayurvedic, traditional Chinese and western medicines.
Under the UK's 1968 Medicines Act, unlicensed herbal remedies may be made up and supplied to an individual patient following a one-to-one consultation with a practitioner. While MHRA says this allowance is "greatly valued by herbal medicine practitioners and by many members of the public", it says there are "weaknesses in the public health protection afforded by the regulatory regime and a number of safety concerns have arisen as a result".
This is not the first time that there has been concern over the safety of ayurvedic products in the UK. In March 2004 a product called Muhayogaraj Guggulu sold by an outlet in London was linked to a case of lead poisoning.
The concern over heavy metal content first surfaced in December 2004 with the publication of an article in the Journal of the American Medical Association, which found that 14 Ayurvedic products sold in the Boston area of the United States contained potentially harmful levels of heavy metals.
Health Canada then surveyed the Canadian market and found that 12 products sold there had dangerously high heavy metal levels.
Last month the American Herbal Products Association in the US made it a condition of membership that companies keep heavy metal levels in supplement products within safe limits.