New data on Pfizer's Chantix drug to help stop smoking raises new concerns about serious side effects, especially for drivers, pilots and others operating heavy machinery, researchers said on Wednesday.
The drug, also known as varenicline, has already been linked to depression and suicide, among other problems.
Shares of Pfizer were down more than 1 percent in extended electronic trading after closing Wednesday at $20.01.
Researchers at the nonprofit Institute for Safe Medication Practices and Wake Forest University said they found hundreds of reported problems since the drug's 2006 approval that included blurred vision, dizziness, confusion and loss of consciousness.
"These data provide a strong signal that the risks of varenicline treatment have been underestimated and show that a wide spectrum of serious injuries are being reported in large numbers," the researchers said.
Chantix works by targeting a certain type of brain receptor affected by nicotine, tobacco's addictive ingredient. The drug blocks some of the effects of nicotine while also providing a nicotine-like buzz to help curb withdrawal.
In a prepared statement, Pfizer said that "the current Chantix label accurately reflects the product's efficacy and safety profile."
"We understand that the Institute for Safe Medication Practices report was based solely on a review of post-marketing adverse event reporting data," the company said. "It is important to understand the limitations of spontaneous adverse event reporting. Often these reports lack sufficient medical information and/or have confounding factors that prevent a meaningful assessment of causality."
FAA Bans Chantix for Pilots, Controllers
The Federal Aviation Administration is banning the use of Chantix by pilots and air traffic controllers after the reports of drowsiness and mood swings.
FAA spokesman Les Dorr says the ban is effective immediately and that the agency was notifying unions representing pilots and controllers. The agency told CNBC that the 180 pilots and controllers it believes to have already taken Chantix will be barred from work for 72 hours, so that the drug can work its way out of their systems.
The FAA decision comes a day after its officials were briefed on the side effects by the Institute for Safe Medication Practices.
- Wire services contributed to this report.