A new study finds that the smoking-cessation drug varenicline (Pfizer's Chantix) has too poor a safety profile to make it suitable for first-line use. Researchers from Wake Forest Baptist Medical Center, and other research centers in the US, found the drug, known as Champix outside the US, was 8 times more likely to result in reports of suicidal behavior or depression than nicotine replacement products. They report their findings in the 2 November issue of PLoS One, an online journal of the Public Library of Science.

The findings contradict those of a recent review by the US Food and Drug Administration (FDA) that found varenicline, which already carries an FDA "black box warning", did not increase the risk of being hospitalized for psychiatric problems such as depression.

In their discussion, the authors suggest one reason for the discrepancy is because they used a different method for analyzing the adverse event data. The proven technique is something called "disproportionality analysis" which is increasingly being used to find links in side effect data that normally escape detection in clinical trials because they occur rarely or there is a level of uncertainty about them.

Another reason is that the FDA review omitted events that did not lead to hospitalization, as study co-author Dr Curt D. Furberg, a nationally recognized leader in drug safety research and a professor of Public Health Sciences at Wake Forest Baptist, explains in a media release:

"Our study contradicts the implications of a recent review by the FDA showing no difference in psychiatric hospitalizations between varenicline and nicotine replacement patches. The FDA hospitalization studies were flawed because they could not capture most of the serious psychiatric side effects, including suicide, depression, aggression and assaults. These can be catastrophic events but do not normally result in hospitalization."

Furberg and colleagues found that 90% of all reported suicides linked to smoking cessation drugs since 1998 involved varenicline, even though the drug had only been on the market for 4 of the almost 13 years they covered.

They also found that varenicline, a non-nicotine drug that works in the brain to block the pleasurable effects of smoking, was 8 times more likely to result in a reported case of suicidal behavior or depression than nicotine replacement products.

"We found that Chantix is associated with more suicidal behavior reports than any other smoking-cessation drug on the US market. The risks simply outweigh the benefits," said Furberg.

For the study, Furberg and colleagues analyzed 3,249 cases of serious injury reported to the FDA's Adverse Event Reporting System from 1998 to September 2010. These included cases of self-injurious behavior or depression linked to varenicline, bupropion (Zyban), an antidepressant approved for smoking cessation, and nicotine replacement products.

Of these, 2,925 (90%) were reported cases of suicidal behavior or depression for varenicline, 229 (7%) for bupropion, and 95 (3%) for nicotine replacement products.

Furberg says while increasing evidence from different sources shows that varenicline substantially increases the risk of psychiatric side effects, we don't know how often these events occur.

Lead author Thomas J. Moore, senior scientist at the Institute for Safe Medication Practices, says:

"While suicidal behavior or depression appear to be prominent side effects of varenicline, they are by no means the only safety issues."

He explains that the drug already carries a warning about the fact studies have found links between its use and aggression and violence.

"Its effects on vision, cognition and motor control and other risks have led to its being banned for airline pilots, air traffic controllers, military pilots and missile crews, and restricted for truck drivers," he adds.

Furberg was also co-author of a study published earlier this year on 4 July in the Canadian Medical Association Journal that found varenicline is also linked to an increased risk of serious cardiovascular events.

He and his colleagues strongly recommend that the FDA change its black box warning so it includes the findings of this study and the FDA's own data. The warning should now show that "varenicline has higher risks for suicidal behavior and depression than other smoking-cessation treatments", says Furberg.

He says they also agree with the US Veterans Administration (VA) who recommend that varenicline should be prescribed only after failure of nicotine replacement, bupropion or a combination, and that smokers should undergo a mental examination to check for risk of suicidal or violent behavior before receiving a prescription.

The Department of Health and Human Services estimates that 36% of American smokers try to quit each year, but only 3% succeed in keeping off tobacco for six months or more, marking smoking as the nation's most treatment-resistant form of drug-dependency.

Written by Catharine Paddock PhD