As of 2014, approximately 5.4 million Canadians smoked daily or occasionally. The fight for smoking cessation has largely been made possible by varenicline, a prescription drug used to reduce the effects of nicotine.

A recent study spearheaded by Andrea Gershon, Lung Health Lead at the Institute for Clinical Evaluative Sciences (ICES) and an associate professor in U of T’s Department of Medicine, pointed to some alarming side effects of varenicline.

According to the study, the use of varenicline is associated with an increased number of serious cardiovascular events in the 12 weeks after starting varenicline use. The study reported a 34 per cent increase in risk of cardiovascular events in patients who had previously experienced cardiovascular episodes and a 12 per cent increase in those who had not.

In this study, serious cardiovascular events referred to heart-related conditions such as heart attacks, insufficient blood flow to the heart, heart failure, ischemic heart disease and stroke, abnormal heart beats, and peripheral vascular disease. The researchers also looked for possible neuropsychiatric effects of varenicline, but no serious effects were observed.

Approximately four patients out of 1,000 experience critical varenicline-induced cardiovascular events. Yet the difference between relative increased risk and absolute increased risk should be noted. “If the risk to begin with is pretty low, then [even with a high relative risk,] the absolute risk will also be low,” said Gershon.

The study was observational in nature, and Gershon took advantage of extensive patient data that was at her disposal. “Every time somebody goes to see a doctor or goes to the hospital, someone or some institution gets paid, and all that information is collected in the large health administrative databases.”

This data, run through the ICES, was collected prior to and after patients went on the medication, and then it was analyzed to determine the rate of incidence of cardiovascular events in patients.

This method was relatively beneficial due to the large sample size, which reduced bias. In general, using observational data can save time and money and increase the study’s scope.

There are, however, limitations — observational studies cannot determine causation. Observational data cannot determine whether patients were using other drugs to help quit smoking, or whether the patients quit smoking while taking varenicline.

Gershon stressed that this study addressed limitations commonly associated with an observational study, and she said that the paper underwent “a very strict peer review” process.

Though the study’s authors suggest that more research is required to confirm their findings, until evidence emerges to prove otherwise, it can be assumed that varenicline does increase the risk of cardiovascular events.

In a 2013 review published by the Cochrane Tobacco Addiction Group, varenicline was found to be the most effective drug for smoking cessation. Smokers were more than twice as likely to quit on varenicline than on a placebo, making it a commonly prescribed smoking cessation aid.

“I think quitting smoking is really important… the benefits of quitting smoking outweigh the risks of this medication,” said Gershon. “It’s complicated — just because somebody takes varenicline, that doesn’t mean they’ll be successful in quitting smoking. How motivated are they? How committed are they? What are their risk factors? It’s hardly an easy decision.”

Every patient is different and extraneous factors such as being predisposed to adverse cardiovascular events will influence how they will react to varenicline.