The safety of Chantix, an anti-smoking pill, is being questioned after reports of serious neuropsychiatric symptoms in some of the drug's users, the Milwaukee Journal Sentinel reported April 18.

The U.S. Food and Drug Administration has issued an alert concerning these symptoms, and Pfizer, the drug's maker, has more prominently warned about them in the drug's information packet. The FDA received reports of 37 suicides related to use of the drug and 491 cases in which people had suicidal thoughts. The FDA also said it "appears increasingly likely that there is an association between Chantix and serious neuropsychiatric symptoms."

Generically known as varenicline, Chantix blocks nicotine receptors in the brain. Nicotine attaches to receptors in the brains of smokers and dopamine is released, giving pleasure. Chantix activates the receptors and blocks nicotine from attaching to them.

"I think the jury is still out on what's going on here," said Carlyle Chan, a professor in the psychiatric department at the Medical College of Wisconsin. Chan said it was unclear whether Chantix caused depression and suicidal thoughts or worsened the symptoms of preexisting depressive behavior. "Be aware that there are some concerns about (Chantix). It needs to be watched closely."

Pfizer, while denying a cause and effect relationship between Chantix and the symptoms, says patients and physicians should be aware of the possibility of these rare serious neuropsychiatric symptoms occurring.