The U.S. Food and Drug Administration (FDA) has confirmed that Pfizer should continue to put the black boxed warning label on its controversial stop-smoking drug Chantix.

Chantix is prescribed twice a day to patients, and its packaging contains one of the strongest warning labels, which has been called the black box, since 2009 as reports have revealed that the drug can cause suicidal tendencies, depression and hostility among patients.

The American drug maker requested the FDA to drop the severe warning on the packaging, suggesting that people taking the drug have side effects similar to other stop-smoking aids.

However, the FDA says that Pfizer has not provided enough evidence to support its claim; hence, the bold letter warning should continue on Chantix's packaging.

"We feel the boxed warning is no longer supported by the data we now have," says Steven Romano, a senior vice president at Pfizer.

An FDA advisory committee with 18 members voted on the inclusion of the label. Only one member supported Pfizer's bid for the removal; 11 members voted that the drug should retain the severe warning while the rest suggested that the wordings be altered.

The FDA normally follows the recommendations of its advisory committee, but the agency can also opt to go against it.

Pfizer's request to remove the label will be reassessed in 2015 following the release of the findings of a study conducted by the drug maker. The study includes 8,000 people taking Chantix, other anti-smoking treatments or none at all.

Chantix was approved by the FDA in 2006 but the warning label was introduced only in 2008. However, in 2009 the FDA recommended that Pfizer embed the warning in a black box. Pfizer was reported to have lost sales due to the introduction of the warning label. The company also faced lawsuits on claims that the drug caused several people to commit suicide.

On the one hand, Pfizer wants to remove the warning label from Chantix and, on the other, some consumer groups such as the Public Citizen, National Center for Health Research and the Institute for Safe Medication Practices have filed petitions with the FDA to strengthen the warning even more.

Diana Zuckerman, president of the National Center for Health Research, says that the advisory committee's decision shows that the warning label should be retained on the packaging.