FDA drops black box warning on Pfizer's anti-smoking drug

The Pfizer logo is seen at their world headquarters in New York (Copyright Reuters 2016)

U.S. health regulators on Friday allowed Pfizer Inc to remove a serious warning from the label of its smoking cessation treatment, Chantix, giving a new lease of life to the controversial drug that was approved a decade ago.

The U.S. Food and Drug Administration slapped a "black box" warning - the most severe available - on Chantix in 2009 after receiving thousands of reports linking the drug to mental health issues, including suicidal thoughts, hostility and agitation.

Pfizer, which has spent heavily on advertising for and settling lawsuits against Chantix, failed to get rid of the warning in 2014 after the FDA decided to wait for additional trial data.

Since then, Pfizer has released data that showed Chantix did not significantly increase the side-effects. The trial had compared either Chantix or GlaxoSmithKline Plc's Zyban with a placebo or a nicotine patch in patients with and without a history of psychiatric disorders.

Based on the data, an independent panel to the FDA in September narrowly voted in favor of removing the warning, arguing that the benefits of Chantix outweighed the demerits of its side-effects and that there was no clear evidence of causality between the drug and the side-effects.

However, FDA scientists had disputed the trial data, flagging multiple inconsistencies in data collection. But when they excluded data they deemed unreliable, the trial results appeared to be consistent with Pfizer's conclusion.

Pfizer said on Friday that the FDA agreed to remove the "black box" warning on Chantix, but said the label should contain the post-marketing reports of the serious side-effects associated with the drug.

The FDA also required that the label mention that Chantix was more effective than other available anti-smoking therapies.

"Especially in patients with mental illnesses, there's been a kind of a barrier in the shape of a box and in the shape of a bias ... so the boxed warning, based on the post-marketing report we felt needed to be clarified," Pfizer Chief Medical Officer Dr. Freda Lewis-Hall told Reuters.

Once touted as a blockbuster, Chantix's sales have dropped from $846 million in 2008 to $671 million last year. The FDA's move comes seven months after European health regulators lifted a similar warning on the drug, called Champix in Europe.

It is very rare for the FDA to rescind a "black box" warning, and critics have raised concerns that such a verdict could set a dangerous precedent.