Pfizer's smoking cessation drug Chantix carries too many risks and should only be tried when other treatments fail, researchers said.
Chantix was eight times more likely to be linked with a reported case of suicidal behavior or depression than other nicotine replacement products, such as the nicotine patch, they said.
The findings contradict two studies released last month by the Food and Drug Administration that showed Chantix (sold as Champix outside the United States) did not increase the risk of being hospitalized for psychiatric problems such as depression.
The agency at the time acknowledged that those studies were flawed because they were too small to identify rare events and they only captured cases that were severe enough to land people in the hospital.
"Our study contradicts the implications of a recent review by the FDA showing no difference in psychiatric hospitalizations between varenicline and nicotine replacement patches," said Dr. Curt Furberg, professor of Public Health Sciences at Wake Forest Baptist Medical Center, co-author of the study published online in the Public Library of Science journal PLoS One.
"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 said in a statement.
Chantix vs. Zyban
The new study relies on adverse events from the FDA's Adverse Event Reporting System from 1998 through September 2010. They analyzed 3,249 reports of serious self-injury or depression linked to Chantix (varenicline), GlaxoSmithKline's Zyban (bupropion) antidepressant that was approved for smoking cessation and nicotine replacement products.
They found that 2,925 cases, or 90 percent, of suicidal behavior or depression reported to the FDA were related to Chantix, even though the drug was only approved for four of the nearly 13 years of data included in the study.
By comparison, there were 229 cases of suicidal behavior or depression related to bupropion and 95 cases related to nicotine replacement products.
"We found that Chantix is associated with more suicidal behavior reports than any other smoking-cessation drug on the U.S. market. The risks simply outweigh the benefits," Furberg said.
Pfizer defended its drug, saying in a statement the analysis relies on reports of serious events to the FDA.
These reports come from a range of sources and often lack important medical information, making them unsuitable for studies such as this, the company said.
"These same authors persist in publishing analyses based on a review of spontaneous reports," Pfizer said in a statement. "It is important to remember that post-marketing reports do not establish a cause and effect relationship between a medicine and a reported adverse event."
Prior studies by Furberg and colleagues have shown Chantix increases the risk of heart problems, unprovoked aggression, and sudden blackouts.
"There were reports of people driving cars and blacking out," said Furberg. He and fellow researchers were so concerned about this side effect that they took their findings to the Federal Aviation Administration, which banned pilots from using Chantix in 2008.
Of course, tobacco use also has serious risks. It is responsible for one in five deaths in the United States each year and adds $193 billion to health care costs.
And quitting is exceedingly difficult.
According to the Department of Health and Human Services, 36 percent of the nation's smokers try to quit each year, but only 3 percent succeed in quitting for six months or more.
Furberg said patients and regulators need to balance the risks of smoking with the benefits of quitting.
But with Chantix, the benefit is slight, Furberg said.
A year after people start taking the drug, only 10 percent of people are off cigarettes, he said.
Chantix carries strong warnings about side effects on its label, but Furberg and colleagues want the FDA to further restrict its use by making it a second-choice drug when other treatments have failed.