An ash tray with cigarette butts is pictured in Hinzenbach, in the Austrian province of Upper Austria, February 5, 2012. Reuters

A new study has debunked the previous reports about the side-effects of Pfizer's quit-smoking drug, which was believed to raise risks of heart attack and depression. The researchers suggest that the quit-smoking drug, Chantix, should be again recommended to smokers aiming to quit, and that the FDA should review its safety warning to the drug to encourage more people on using it.

The study, published in the journal Lancet Respiratory Medicine, shows that the previous studies have failed to provide any evidence on the potential side effects of Chantix on mental health and the heart. For the study, the researchers analysed random health information from more than 150,000 smokers in England.

The participants were monitored for six months to assess any impact of the drug on their health. The team found that the treatment with Chantix, also known as varenicline, does not cause any symptoms of heart attack on those who have used nicotine replacement therapy or another quit-smoking drug.

The treatment was also found not to raise the risk of depression, self-harm and suicide on the patients, the researchers said.

After Pfizer first launched the drug in 2006, reports followed that Chantix caused changes in behaviour, depressed mood and suicidal thoughts on patients after several weeks of treatment. Other reports added that patients suffer from seizures and heart attacks after taking the drug.

The reported problems led FDA officials to ask Pfizer to update the drug label to include the health warnings. But the researchers of the new study suggest that doctors can now prescribe varenicline to a wider range of smokers.

"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," said Professor Daniel Kotz from the Medical Faculty of the Heinrich-Heine-University Dusseldorf, in a press release. Chantix is known as the most effective treatment to help people quit smoking.

The effectiveness of the drug reduces the craving for and pleasurable effects of cigarettes, and the heavy smokers who find it difficult to quit are those who commonly use the prescription of varenicline. In the United States and Britain, Chantix is one of the biggest-selling stop-smoking drugs that generated $647 million in revenue in 2014.

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

However, smokers could use other methods to quit. Experts say counselling, behavioural therapies and medications may also aid to drop their smoking habit, and today, there are more former smokers than current smokers.

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