Anti-smoking drug has serious side effects: FDA

WASHINGTON -- U.S. regulators Friday said Pfizer Inc's anti-smoking drug Chantix appears increasingly likely to be linked to serious psychiatric behavior, and called for stronger label warnings.

The Food and Drug Administration said after an analysis of reports of suicidal thoughts and behavior potentially linked to the medication, it was calling for Pfizer to boost the prominence of label warnings on the drug.

"It appears increasingly likely that there may be an association between Chantix and serious neuropsychiatric symptoms," the FDA's Public Health Advisory said.

Chantix, approved in 2006, already carries a warning that some patients have experienced psychiatric symptoms, including depressed mood and suicidal thoughts, while on the drug.

The FDA in November issued an "early communication" on the drug, saying it would analyze reports of suicidal thoughts and other unusual behavior.

The drug has been prescribed to about 4 million people in the United States, according to Pfizer.