The researchers, who reviewed 14 studies on Chantix, found a 72% increase in these events compared to smokers taking a placebo.
The study is published in the Canadian Medical Association Journal.
"Action needs to be taken by the company," says study researcher Sonal Singh, MD, MPH, referring to Pfizer, the maker of Chantix. "They need to put accurate safety information on the label."
In a statement, Pfizer points out that only 1.06% of the nearly 5,000 people in the analysis taking Chantix reported a problem compared to 0.82% of the people taking placebo.
"The actual difference in cardiovascular event rates seen in the Singh analysis was less than one quarter of one percent," the statement notes. "The analysis contains several limitations; most notably that it is based on a small number of events, which raises concerns about the reliability of the authors' conclusions."
Singh, an assistant professor of medicine at Johns Hopkins University, says safety concerns led him to stop prescribing Chantix a year ago.
This is not the first time that the safety profile of Chantix has been called into question. A black box warning, the FDA's most serious safety warning, was added to the Chantix label in 2009 due to concerns of a link with suicidal thoughts and behaviors, depression, hostility, and other behavioral changes.
The new study finds that Chantix users with no previous history of cardiovascular disease are also at increased risk of serious problems.
In their analysis of data from 14 studies, the researchers found that 52 out of the 4,908 men and women taking Chantix experienced a serious cardiovascular event, such as heart attack, abnormal heart rhythm, stroke, heart failure, or related death, compared to 27 out of the 3,308 in the placebo group. That led the authors to conclude that Chantix raised the risk of serious cardiovascular problems by nearly 72% compared to placebo.
"Our findings have potential regulatory and clinical implications," the researchers conclude.
Tina Kaufman, PhD, an assistant professor of medicine and smoking cessation coordinator at Oregon Health and Science University, says that while the study does raise important safety concerns that doctors should discuss with their patients, the results are not likely to change prescribing practices among the cardiologists with whom she works.
"We're talking about a small risk compared to the huge benefits of quitting," says Kaufman, who was not involved in the study. "It's far more dangerous for them to continue smoking."