New research suggests that Pfizer’s controversial quit-smoking drug Champix may not increase the risk of heart attacks or depression, contrary to previous reports.

The study, published in the Lancet, tracked over 150,000 smokers in England over six months. It found that those taking Champix (varenicline), which is marketed as Chantix outside of Europe, were at no higher risk of depression or suffering a heart attack than those using other drugs or nicotine-replacement therapy.

"Regulators such as the Food and Drug Administration (FDA) should review their safety warnings in relation to Champix as this may be unnecessarily limiting access to this effective smoking cessation aid," says Aziz Sheikh, one of the study’s authors and co-director at the University of Edinburgh’s Centre for Medical Informatics.

The FDA previously required Pfizer to put boxed warnings on the drug to highlight the risks of neuropsychiatric (NPS) and cardiovascular adverse events in 2009 and 2011 respectively. There have been over 3,000 lawsuits relating to Chantix in the US.

The drug is one of the biggest-selling smoking cessation drugs in the US and the UK, bringing $647 million in sales for Pfizer in 2014. However it has seen a steady decrease in sales since the controversy began, down from $883 million in 2007.