A new study debunks an earlier belief that Pfizer's stop-smoking drug increases one's risks of heart attack and depression. Chantix is a drug manufactured by Pfizer to help adults quit smoking. Earlier studies have linked the drug to changes in behavior, depressed mood and suicidal thoughts after several weeks of taking the drug. There were also reports of seizures and heart attacks. In March this year, the FDA asked the drug maker to update the drug label to include these health warnings.

Pfizer worked with researchers from several universities to determine whether the stop-smoking drug really triggers heart attack and depression among users. The study involved more than 150,000 smokers who were grouped into three: those prescribed with the stop-smoking drug, a group given another anti-smoking drug called bupropion (also an anti-depressant), and a group that used nicotine replacement therapy such as patches, chewing gum or lozenges. The researchers assessed them after six months for improvement.

The analysis showed that the Chantix and the other anti-smoking drug do not increase one's risk of heart attack and depression.

"Smokers typically lose three months of life expectancy for every year of continued smoking. Our research supports the use of varenicline as an effective and safe tool to help people quit," Daniel Kotz, study co-author from the medical faculty of the Heinrich-Heine-University Dusseldorf, said in a press release.

The researchers recommend that the FDA should revisit its safety warning to the stop-smoking drug so that more people would consider using it.

"Regulators such as the United States Food and Drug Administration (FDA) should review its safety warning in relation to varenicline as this may be unnecessarily limiting access to this effective smoking cessation aid," Aziz Sheikh, co-director of the University of Edinburgh's Centre for Medical Informatics, added.

Seven out of 10 adult cigarette smokers said in 2010 that they wanted to quit smoking, according to the CDC. There are different ways that could help smokers drop the habit including counseling and behavioral therapies and medications. To date, there are more former smokers than current smokers.

The study was published in Sept. 6 issue of The Lancet Respiratory Medicine.