Spangler alerted the FDA to potential safety concerns back in 2007 when he discovered that a small study widely quoted as showing that Chantix was safe to use for up to a year was in fact misleading. When he ran the numbers the authors reported, he found that those on Chantix for a year had 2.5 times the risk of serious adverse events, including cardiovascular events, as those on placebo.
In the five years since Chantix was approved, it has been the subject of several FDA safety reviews, most notably one concerning depression, suicidal thoughts and suicidal actions -- adverse effects that earned Chantix the FDA's strongest "black box" warning label in 2009.
It wasn't until earlier this month, however, that the FDA publicly acknowledged a potential link between Chantix and cardiovascular issues after reviewing a 2010 study led by Dr. Nancy Rigotti, a professor at Harvard Medical School and the director of Mass General's Tobacco Research and Treatment Unit, which looked at cardiovascular risk and Chantix.
The FDA contends that the Rigotti study was the first to raise significant concern over cardiac risk, as the other studies showed negative cardiac effects on Chantrix that were "fragile" and "not something we would label on," says Curtis Rosebraugh, director of the Office of Drug Evaluation II at the FDA.
Pfizer said in a statement to ABC News that it disagrees with Singh et al's interpretation of the data, arguing that the actual number of heart attacks and other cardiac events were too small to determine if Chantix was the cause.
Because of the FDA's plans to amend the label information, however, the agency has already asked the pharmaceutical company to turn over all its data concerning Chantix and adverse cardiac events so that the FDA can perform its own in-depth analysis of the drug's safety profile. That profile will use, among other sources, the 14 studies evaluated in Singh's meta-analysis.
"Had we not already been working on our own analysis, Singh's analysis would have raised concerns. As it is, it underscored our own concerns," says Celia Winchell, medical team leader of addictive products at the FDA.