Pfizer has come out with a staunch defence of its underfire smoking cessation drug Chantix, which was the subject of a recent study claiming that the drug has been linked to 3,000 reports of adverse events.

The study in question came from the nonprofit Institute for Safe Medication Practices organisation and analysed the side effects associated with Chantix (varenicline) that have been reported to the US Food and Drug Administration. The ISMP noted that these included 227 reports of suicidal acts, thoughts or behaviours, 397 cases of possible psychosis and 525 reports of hostility or aggression and the results led the US Federal Aviation Administration to bann use of Chantix by pilots and air traffic controllers.

However, speaking to reporters in New York, Pfizer defended the product's safety and effectiveness and chief medical officer Joseph Feczko noted that more than 90% of the reported adverse events have already been discussed with FDA some time ago. Gretchen Dieck, the firm's head of safety and risk management, also noted that the ISMP report has not been published in a peer-reviewed journal and the number of reported incidents do not necessarily represent a true safety signal.

David Gonzales, co-director of Oregon Health & Science University's Smoking Cessation Center who led some pivotal studies of Chantix, noted that "patients in the trials are not terribly reflective of the population of smokers." Interestingly he also added that smokers with psychiatric problems were excluded from placebo controlled trials due to fears of exacerbating their conditions but exist in large numbers in the general population.

Dr Gonzales added that "the safety profile of this drug is particularly good," but he noted that no more than 5% of people who attempt to quit smoking without drugs or nicotine replacements are successful. He also noted that any of the smoking cessation treatments "out there are substantially better than doing it on your own".

Pfizer concluded by saying that it does not believe the Chantix label needs stronger safety warnings and Ms Dieck claimed "we strongly believe that the current label really reflects what is the current evidence with regards to the safety and efficacy profile of the product". First-quarter sales of Chantix soared 71% to $277 million but how badly the recent adverse publicity hits revenues will become apparent very soon.