Tong Ren Tang Technologies Co, a leading traditional Chinese medicine (TCM) producer in China, announced on its website Thursday that it has never ­exported Niu Huang Jie Du Pian ­medicine to the UK and Sweden or sold the medicine online, and it will further investigate the warning on the medicine issued by the UK's medicine regulator.

The UK-based Medicines and Healthcare ­Products Regulatory Agency (MHRA) warned on its website Tuesday that ­several dangerous and unlicensed TCMs contain high levels of heavy metals such as lead, mercury and arsenic.

According to the warning, Niu Huang Jie Du Pian, a medicine used for treating infections and inflammation produced by Tong Ren Tang, contains extremely high level of arsenic.

The Swedish National Food Agency also found large amount of arsenic in the medicine, the MHRA's announcement said.

The MHRA said that none of these medicines are licensed or authorized for sale in the UK, but they have been sold on the Internet.

Tong Ren Tang's brand management department refused to comment on the issue when reached by the Global Times Thursday.

A Chinese medicine expert told the Global Times Thursday on condition of anonymity that TCM is made of plant, animal or mineral ­substances, which contain something ­hardly found in Western medicines ­using chemical substances.

Arsenic in Niu Huang Jie Du Pian comes from realgar, a main mineral ingredient of the medicine, and can be harmful to health if used excessively, the expert said, noting that it is safe to take the medicine as long as it is not taken in large amounts for a long period of time, and doctors will also not advise patients to do so.

Wang Yuedan, vice director of the Immunology Department with Peking University, wrote in an article on his blog Wednesday that each tablet of the medicine contains about 0.011 grams of arsenic, so he speculated that there can be an obvious damage to people's health only if the intake reaches 800 tablets per day lasting for two years, based on arsenic experiments on mice.

According to information from China Food and Drug Administration (CFDA) website, the medicine has got the regulatory approval.

The CFDA could not be reached Thursday.

The MHRA's warning also involves two other TCM products made by Chinese firms which contain dangerously high level of heavy metals.

Before this warning, there have been five other cases about quality problems on Tong Ren Tang's products this year, including illegal ingredients and substandard quality. Some products have been recalled or banned in the Chinese mainland and Hong Kong markets.