Pfizer’s Chantix (varenicline) looks be better than GalxoSmithKline's rival Zyban (bupropion) in helping smokers give up the fags and then stay off them, according to recent clinical trial data unveiled in the Journal of the American Medical Association.

One study assessed Chantix and Zyban (an antidepressant also sold as Wellbutrin) against a placebo in 1,025 smokers and found that, after 12 weeks of therapy, 44% off people taking Chantix were off the cigarettes, compared to 29.5% in the Zyban group and 17.7% taking a placebo.

But the researchers noted that, after 12 months, the abstinence rate for Chantix (21.9%) was not all that different from Zyban (16.1%), although both substantially overshot the placebo group rate of 8.4%. In direct contrast, however, a second study demonstrated that Chantix induced a significantly greater abstinence rate than Zyban, with 23% versus 14.6%, respectively.

The results are certainly encouraging, but an accompanying editorial warns that smokers should not to pin their hopes on this drug being the holy grail of smoking cessation. “There are some important gastrointestinal side effects and, in the current studies, most people given the drug actually did not quit smoking,” co-author Dr Robert C Klesges, from the University of Tennessee, Memphis, told Reuters Health. This indicates that, while the drug might be the best smoking cessation aid on the market, other factors, such as behavioural changes, need to be addressed if the patient wants to quit for good.

Chantix was given the all clear by US regulators in May, representing the first prescription anti-smoking medication to be approved in more than 10 years, according to media reports. The agent has a unique mode of action involving a dual approach to helping smokers quit; it blocks the pleasure receptors in the brain associated with cigarette smoking and nicotine, and cuts the level of withdrawal symptoms that often drive a return to the addiction.

The need for an effective drug to help smokers kick their habit is greater than ever. In the USA, it is responsible for one in five deaths and costs the US healthcare system some $167 billion every year. And, according to the Centers for Disease Control and Prevention, an estimated 44.5 million adults in the USA smoke cigarettes and more than 8.6 million of them have at least one serious illness caused by smoking.

Pfizer filed for European approval of varenicline in November 2005, and looks set to have a clear run at the market for a while at least, after US and European regulators put the clamp on Sanofi-Aventis' pill Acomplia (rimonabant) for smoking cessation - although they gave it a nod for treating obesity. Analysts have forecast peak sales for Chantix of $500 million to $1 billion.