Researchers from the U.K.'s drug regulatory agency and the University of Bristol compared the incidence of suicide and self-harm among smokers taking Chantix to that of smokers using the drug Zyban or nicotine-replacement products to help them give up cigarettes.
Last July, the FDA announced it would require labeling for Chantix and Zyban to include its strongest safety message, warning that people taking the drugs should be closely watched for signs of suicidal thoughts, hostility, and depressed mood in users.
At a news briefing, an FDA official said 98 suicides and 188 suicide attempts had been reported among people taking Chantix since the drug was approved for sale in the U.S. in 2006.
Using data from a medical registry with roughly 3.6 million people living in the U.K., epidemiologist David Gunnell, PhD, and colleagues identified 80,660 adults who were prescribed smoking-cessation products between September 2006 and May 2008.
About three-quarters of the prescriptions were for nicotine-replacement therapies, including patches, inhalers, gum, tablets, or lozenges. Slightly fewer than 11,000 prescriptions were for Chantix and around 6,400 were for Zyban.
Using electronic medical records, the researchers searched for evidence of fatal and non-fatal self-harm, suicidal thoughts, and depression over the period in which the treatments were used up until three months after the last prescription was filled.
After controlling for known risk factors for self-harm and depression, the researchers found no clear evidence of an increased risk of self-harm, suicidal thoughts, or depression in Chantix users or users of any of the other products.
"This is the first study to look at this question in detail, and the results are largely reassuring," Gunnell tells WebMD. "Our best estimate is that if there is an increase in the risk for fatal and non-fatal self-harm associated with [Chantix] the risk is likely to be very small."
Gunnell says larger studies are needed to further quantify the risk. "Any such risk has to be balanced against the risks associated with continuing to smoke."
The study was paid for by the U.K.'s drug regulatory group, the Medicines and Healthcare Products Regulatory Agency (MHRA).
It was published today in the journal BMJ Online First.
In a statement issued Thursday afternoon, a spokeswoman for Pfizer Inc., which markets Chantix in the U.S., told WebMD the company considers the overall risk-benefit profile of the drug to be 'favorable."
She added that the company is conducting clinical trials of the drug in patients with psychiatric disorders as well as other patient populations.