Smokers seeking medical help to quit are being monitored after reports linking the anti-smoking drug Zyban to 18 deaths in the UK.
The Department of Health says the deaths are not necessarily a result of using the drug, because the people who died may have had serious underlying health conditions.
The tablets have been used by more than 250,000 people in Britain since the treatment was introduced last year.
A spokeswoman for the manufacturer, GlaxoSmithKline, said more than 15 million people have taken the drug worldwide and clinical trials had found no evidence of increased risk of death.
The drug was hailed as a major breakthrough in helping smokers to beat their addiction.
The pill acts on the brain to quash the craving for nicotine that tobacco products produce.
It is the first anti-smoking medication licensed in the UK that does not contain nicotine itself.
Every hour 13 people die in the UK from smoking-related diseases - a quarter of these in middle age.
A survey has shown that more than two-thirds of smokers (68%) want to give up.
A study published in the New England Journal of Medicine last year found that almost one in three people treated with Zyban were not smoking at one year.
Zyban was found to be almost twice as effective as a nicotine patch in helping people to quit smoking and to stay off tobacco for at least one year.