New research suggests that a highly effective drug that helps smokers to quit does not increase their risk of heart attack and depression as was previously thought.

Researchers from the University of Edinburgh say doctors can prescribe varenicline -- also known as ChampixTM or ChantixTM -- more widely to help people stop smoking after failing to find any evidence that varenicline has a negative effect on mental health. It also shows that taking the drug does not raise a person's risk of heart disease.

"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," researcher Daniel Kotz said in a statement.

For the study, researchers looked at anonymized health information from more than 150,000 smokers across England.

The patients had been prescribed either varenicline or another anti-smoking drug called bupropion to help them quit, or had used nicotine replacement therapy - such as patches, chewing gum or lozenges. They were tracked for six months to assess any impact of the treatment on their health.

Researchers found that people taking either varenicline or buproprion were no more likely to suffer a heart attack than those using nicotine replacement therapy. They also found people were also not at higher risk of depression or self-harm.

"On the basis of our extensive analysis, we believe it is highly unlikely that varenicline has any significant adverse effects on cardiac or mental health. 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, researcher and co-director of the University of Edinburgh's Centre for Medical Informatics, said in a statement.

The findings are detailed in The Lancet Respiratory Medicine.