A globally popular drug used to help smokers quit could be doing more harm than good, according to observational research out of Canada—while the medication can more than triple a smoker’s chances of nixing the habit, it could also substantially increase the risk of experiencing a cardiovascular event.

Varenicline—known colloquially as Chantix in the U.S. and Champix in Europe and Canada—is commonly prescribed to individuals aiming to quit tobacco, lead author Andrea S. Gershon, MD, and colleagues wrote in the American Journal of Respiratory and Critical Care Medicine. But while its proven efficacy makes the drug appealing, Gershon and her team found that in heart patients, taking varenicline could raise the risk of adverse cardiovascular events by as much as 34 percent.

For their research, Gershon et al. analyzed the medical records of 56,851 new varenicline users between 2011 and 2015. All patients were Ontario-based and acted as their own controls; since varenicline is generally taken for 12 weeks, clinicians tracked each patient from the weeks prior to starting the medication through the weeks following stoppage. 

While patients who’d experienced cardiovascular complications in the past were more than 30 percent more likely to have a myocardial infarction, stroke, arrhythmia, unstable angina and peripheral vascular disease, that figure was just 12 percent in individuals with a clean bill of health. Still, Gershon’s work resulted in a firm figure: among all patients, there were 3.95 adverse cardiovascular events per 1,000 varenicline users that could be attributed solely to the drug.

“This is a figure that physicians can quote to their patients,” the study reads.

The team also found a slight, nonsignificant relationship between varenicline usage and increased trips to the emergency room for neuropsychiatric symptoms like depression, anxiety, psychosis, hallucinations, insomnia and self-harm.

Gershon said in a release from the American Thoracic Society her work was prompted by a lack of cohesive research in the field.

“Previous studies regarding the safety of varenicline have been conflicting and most examined people with relatively similar characteristics and backgrounds in highly controlled settlings,” she said. “We wanted to study varenicline among all kinds of people in the world.

Of the more than 55,000 patients she and colleagues tracked, Gershon reported 4,185 and 4,720 patients experienced one or more adverse heart or neuropsychiatric events during the trial, respectively.

Gershon recommended in the release doctors may want to monitor heart patients taking varenicline more closely, but the American Thoracic Society emphasized this research is observational and self-controlled, therefore “cannot determine cause and effect.” 

Still, Gershon and co-authors wrote, varenicline is an option that should be weighed for each individual patient, since it can be largely effective in quitting smoking.

“Quitting smoking greatly reduces a person’s chances of developing heart disease and cancer and has many other health benefits,” she said. “Our findings should not be used to suggest people not take varenicline. The findings should be used to help people make an informed decision about whether they should take varenicline based on accurate information about its risks as well as its benefits.”