Nicotine chewing gum, lozenges and inhalers designed to help people to give up smoking may have the potential to cause cancer, research has suggested.

Scientists have discovered a link between mouth cancer and exposure to nicotine, which may indicate that using oral nicotine replacement therapies for long periods could contribute to a raised risk of the disease. A study funded by the Medical Research Council, led by Muy-Teck Teh, of Queen Mary, University of London, has found that the effects of a genetic mutation that is common in mouth cancer can be worsened by nicotine in the levels that are typically found in smoking cessation products.

The results raise the prospect that nicotine, the addictive chemical in tobacco, may be more carcinogenic than had previously been appreciated. “Although we acknowledge the importance of encouraging people to quit smoking, our research suggests nicotine found in lozenges and chewing gums may increase the risk of mouth cancer,” Dr Teh said. “Smoking is of course far more dangerous, and people who are using nicotine replacement to give up should continue to use it and consult their GPs if they are concerned. The important message is not to overuse it, and to follow advice on the packet.”

Most nicotine replacement products have labels advising people to cut down after three months of use and to stop completely after six months.

Mouth cancer affects nearly 5,000 people each year in Britain and is usually linked to smoking, chewing tobacco or drinking alcohol. It is often diagnosed at a late stage, and consequently has a poor prognosis.

Although nicotine is acknowledged as the addictive element in cigarettes its role in cancer has long been disputed. It is not as potent a carcinogen as other chemicals found in tobacco smoke, such as tar, but some previous research has suggested that it may also contribute to the formation of tumours.

Nonetheless, it is much less dangerous than cigarettes and is therefore used in a wide variety of smoking cessation products that allow addicts to satisfy a craving for the chemical without smoking.

In the new research, published in the journal Public Library of Science One, Dr Teh’s team has investigated the role of a gene called FOXM1 in mouth cancer.

A mutation that raises the activity of this gene is commonly found in many tumours, and is also present in pre-cancerous cells in the mouth, the scientists found. This raised expression can then be worsened by exposure to nicotine, according to Dr Teh.

“If you already have a mouth lesion that is expressing high levels of FOXM1 and you expose it to nicotine, it may add to the risk of converting it into cancer,” he said. “Neither the raised FOXM1 nor nicotine is alone sufficient to trigger cancer, but together they may have an effect.

“The concern is that with smokers, you are looking at people who are already at risk of oral cancer. I’m worried that some may already have lesions they don’t know about in the mouth, and if they keep on taking nicotine replacement when they stop smoking products they will not be doing themselves any good.”

The findings could also lead to new ways of diagnosing mouth cancer while it is still in its early stages and easier to treat.

Dr Teh emphasised that smokers should not stop their attempts to give up. “There is no doubt about the harmful effects of smoking, so smokers should make every effort to quit.”

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