Pfizer updated the Chantix label in US by including a new warning that says the patients who are taking this drug should be observed for serious neuropsychiatric symptoms, including changes in behavior, agitation, depressed mood, suicidal ideation and suicidal behavior.

The warning is similar with the one included in November last year, but the language is more prominently located to better get the attention of doctors.

Varenicline, also known as Chantix, a pill prescribed for those who want to quit smoking has been sold in United States from August 2006, after it was approved in May 2006. Since its introduction, Chantix generated about $600 million in sales.

In November last year the U.S. Food and Drug Administration revealed that it had received reports of mood disorder and erratic behavior among patients using Chantix.

FDA advised doctors to closely supervise their patients and report whether they have any behavior changes. The federal agency said that the changes have often been reported within days or weeks of people first taking the drug. FDA announced in November that it is investigating at least one incident of a patient who died while being under Chantix treatment.

Although it has agreed to include the warning since November, Pfizer said that there is no scientific evidence linking Champix to depression.

“A causal relationship between Chantix and these reported symptoms has not been established. In some reports, however, an association could not be excluded. More specifically, some reports may have been complicated by the symptoms of nicotine withdrawal in patients who stopped smoking, but not all patients with these symptoms had quit smoking,” Pfizer said in a statement released today.

Pfizer noted that in the controlled clinical trial program of more than 5,000 patients treated with Chantix, changes in behavior, agitation, depressed mood, suicidal ideation, and suicidal behavior occurred at a rate comparable to placebo-treated patients. There were no suicides attributed to CHANTIX in clinical trials.

In December last year, the European Medicines Agency (EMEA) said Pfizer’s Champix, (the European name of Chantix), should carry a warning about the high risk of suicide attempts among patients. The Committee for Medicinal Products has closely monitored the safety of the drug for Human Use (CHMP) since it was first authorized in the European Union in September 2006.

Last year, Selena Bartlett, a neuroscientist at Ernest Gallo Clinic and Research Center at University of California, revealed after a study conducted on rats that Chantix might also reduce drinking addiction.