Almost no one believes it’s easy to quit smoking, so when the drug Chantix hit the U.S. market in May 2006, some smokers breathed a sigh of relief they had finally found a way out from the grip of cigarettes.

Chantix works by blocking the pleasant effects of nicotine on the brain of the smoker. It also claims to lessen the uncomfortable withdrawal symptoms.

But there were the Chantix dreams – sort of bizarre, unworldly hallucinations awake or asleep. There have been suicides, aggressive behavior, assaults, even homicides associated with use of the drug. The behavior was so pronounced that pilots and truck drivers were banned from using Chantix.

An updated review just released by the U.S. Food and Drug Administration (FDA) finds Chantix (varenicline) may increase the risk of heart attack. Drugmaker Pfizer conducted the analysis and found a higher risk of cardiovascular events including myocardial infarction (MI) and stroke, than with a placebo.

Among the 4,190 smokers studied, 13 had a heart attack or stroke compared to six among the 2,812 on the placebo, reports the FDA. However the agency says the events are not statistically significant.

This is not the first time varenicline has been associated with cardiovascular events. The label for Chantix was upgraded in June 2011 to warn about heart problems which sparked this FDA meta-analysis (combined analysis). The label was changed in 2009 when the FDA ordered Pfizer to warn of depression, suicide and neuropsychiatric symptoms.

During the first quarter of 2008, the FDA reported Chantix topped the list of most dangerous drugs. There had been more than 20,000 serious injury reports and 4,824 deaths associated with use of the smoking cessation drug.

In July 2011, the Canadian Medical Association Journal published a Johns Hopkins study linking an increased “risk of serious adverse cardiovascular events associated with varenicline.”

One year later, researchers from the University of California San Francisco (UCSF) questioned that conclusion and the methodology used by Johns Hopkins that found a 72 percent relative risk of heart problems. The UCSF analysis found a 0.27 absolute risk difference, which is not statistically significant.

Since smoking is already a risk for heart disease, cancer, and stroke, the FDA will need to determine whether the benefit of quitting is worth the risk of cardiovascular events.