Researchers have found that people who take stop-smoking prescription drug Champix (varenicline) are more likely to suffer heart attacks and stroke.
As part of the study, published in the Canadian Medical Association Journal, researchers looked at 14 clinical trials involving over 8,000 people.
The pill, which accounted for 955,242 prescriptions in England last year, was found to put people at a higher risk of being admitted to hospital with a serious cardiac event.
Dr Sonal Singh, from the Johns Hopkins University School of Medicine in Maryland in the US, who worked on the study, said: "Among tobacco users, varenicline use was associated with a significantly increased risk of serious adverse cardiovascular events greater than 72%."
Concerns have been raised in the past over the effects of the drug, after feelings of depression, suicidal thoughts and anxiety were reported by patients who took the pill.
"Smokers are high risk for CV events, more research needs to be done, in order to state categorically that varenicline increases risk" - H Reece, Wiltshire
"What are the risks if they continued to smoke?" - Jane, Cambs
"These people are already high risk due to their smoking habits. Who can say it would not have happened in any case. What's the evidence in regard to their other risk factors" - Annette Turner, Thornaby
"Surely if you smoke you are increased risk. We don't do angios/ECG before starting treatment" - Christine Allison, Lewisham