The US Food and Drug Administration says that Pfizer's smoking cessation drug Chantix may be associated with "a small, increased risk of certain cardiovascular adverse events" in patients who have heart disease.

The information will be added to the label for Chantix (varenicline), which is known as Champix in Europe. It already carries a warning about raising the risk of suicide.

The FDA reviewed a trial of 700 smokers with cardiovascular disease who were treated with Chantix or placebo and the Pfizer drug was effective in helping patients quit smoking and remain abstinent for as long as one year. The agency notes that cardiovascular adverse events were infrequent overall, but certain reactions, including heart attack, were reported more frequently in patients treated with Chantix than those on placebo.

The FDA added that it is continuing to evaluate the cardiovascular safety of Chantix and is requiring Pfizer to conduct a meta-analysis of its existing trials.

Chantix is a good earner for Pfizer and first-quarter sales reached $233 million, up 32%. A couple of years ago, however, the drug's image suffered amid fears it could increase the risk of suicidal acts, thoughts or behaviours, psychosis and hostility or aggression.