A popular smoking-cessation medication may be linked to an increased risk of cardiovascular problems, a new study has found, adding to questions about the drug's safety.
Research published in the Canadian Medical Association Journal on Monday shows that people who took varenicline were more likely to experience "serious adverse cardiovascular events," such as an irregular heart beat, heart attack or stroke, than people who took a placebo.
"If you're a smoker and you're thinking of quitting, there are cheaper and safer ways to quit smoking," said Sonal Singh, an assistant professor of medicine at Johns Hopkins University School of Medicine and lead author of the study.
Varenicline, sold under the brand name Champix in Canada and Chantix in the United States, helps to reduce nicotine cravings and withdrawal symptoms. It was heralded by many experts as a potential breakthrough smoking-cessation drug until many safety questions began to emerge. Worldwide sales of the drug last year were $755-million.
The drug has already been flagged by regulators around the world for psychiatric side effects, including suicidal thoughts and behaviour.
Health Canada, which approved the drug for sale in 2007, has issued several warnings, telling patients and health-care professionals that it may be linked to depression, agitation, aggression, hostility and thoughts of self-harm. As of last year, Champix must carry a boxed warning, which is reserved for drugs with serious safety issues or adverse events.
But new research suggests that Champix may also pose risks to the heart.
In June, the U.S. Food and Drug Administration announced that the drug may be linked to a "small, increased risk" of cardiovascular side effects in people who already have cardiovascular disease. The decision was made after officials reviewed a clinical trial of 700 smokers with cardiovascular disease and found that cardiovascular risks to patients taking Champix was 2 per cent, compared with 1 per cent for individuals not taking the drug.
The agency is adding a new warning on the drug's label to reflect the risks and is conducting a safety evaluation. It is also requiring Pfizer, which manufactures Champix, to conduct a large study to determine the significance of the heart risks.
After the FDA made the announcement, Health Canada said it will also investigate Champix and its potential links to heart problems.
In the new study, Dr. Singh and his colleagues reviewed data from 14 clinical trials and found that patients taking Champix faced a 72-per-cent increased risk of heart-related adverse events.
Specifically, the authors identified 52 serious cardiovascular events among 4,908 patients taking Champix, compared with 27 cardiovascular events among 3,308 individuals who took a placebo.
Dr. Singh said the results raise important questions about the potential dangers many patients face if they take the drug. "This is just like driving a car without brakes," he said. "Going forward, I don't know how we will convince our patients to take Champix for what, to increase your risk for heart attack?"
Health Canada notes on its website that heart-related side effects have occurred "rarely" in clinical trials studying Champix, and said that information is included in the drug's prescribing information.
But Dr. Singh argued that the heart risks are being underplayed and that federal regulators, such as Health Canada and the FDA, have an obligation to warn patients and take action. "The regulators need to take responsibility for this issue," he said.
Pfizer Canada disputes the study's findings, saying in a statement that the number of cardiovascular events suffered by patients is too small to be considered significant. The company also highlighted the serious risks posed by smoking and said Champix can help people who want to quit.
A commentary published with the new study echoed Pfizer's statement, focusing on the limitations and potential weaknesses of Dr. Singh's research. The risks of the drug are "greatly outweighed by the benefits of diminishing the truly 'heartbreaking' effects of smoking," wrote Taylor Hays, who studies tobacco dependence at the Mayo Clinic.
But Dr. Singh noted that Dr. Hays has been paid by Pfizer to conduct research on Champix and criticized the CMAJ for publishing a commentary written by someone affiliated with the drug company instead of an independent expert. "They couldn't find any tobacco researcher in Canada that doesn't get money from Pfizer?" he said.