Source: Pfizer. 

Pharmaceutical juggernaut Pfizer (PFE 0.87%) has a storied history of developing and selling game-changing therapies. To date, cholesterol lowering drug Lipitor is still the best-selling drug of all time, with more than $140 billion in lifetime sales. Pfizer also brought the world osteoarthritis and rheumatoid arthritis drug Celebrex and nerve-pain therapy Lyrica.

But, Pfizer's history has had its share of misses and disappointments. One such disappointment is Chantix, an oral therapy used in conjunction with support, counseling, and educational materials to help people quit smoking.

Pfizer's biggest disappointment?
On paper, a Food and Drug Administration-approved therapy to help people quit smoking should be instant gold. Despite adult smoking rates falling for nearly five decades, from 42% to 18% according to the Centers for Disease Control and Prevention, there are still in excess of 42 million adults lighting up in the United States. That represents a wide moat of potential patients for Pfizer and Chantix. Unfortunately for Pfizer and its shareholders, the promise of Chantix has never come close to its actual results.

In July 2009, the FDA announced that it would be requiring Pfizer and GlaxoSmithKline, the maker of Zyban, the only other FDA-approved product for smoking cessation, to place black box warnings on their packaging highlighting potentially serious mental health changes that could occur while taking these drugs. The FDA notes that depression, hostility, and suicidal thoughts are among the most dangerous mental changes physicians should be on the lookout for. Following reports of unusual changes in behavior, the FDA observed that cessation of the drugs themselves resulted in a reversal of the aforementioned behaviors.

Source: Centers for Disease Control and Prevention. 

Were that not enough, in June 2011 the FDA issued new safety information regarding Chantix, noting that it "may be associated with a small, increased risk of certain cardiovascular adverse events in patients who have cardiovascular disease." The FDA required Pfizer to add this concern to its warning label for Chantix.  

Even more recently, in March of this year the FDA again update Chantix's label to reflect a warning that Chantix can change the way users react to alcohol. The FDA pointed out in its press release that rare accounts of seizures in patients treats with Chantix were reported, although no concrete data pinpointed Chantix as the cause.

With the deck of health concerns stacked against Chantix, instead of being a multi-billion blockbuster, it has been relegated to just $332 million in worldwide sales through the first-half of 2015, a 10% operational increase from the prior-year period. But, is Chantix's fortune about to change for the better?

Could this study put Chantix's worries to rest?
According to professor Aziz Sheikh, a professor and co-director at the University of Edinburgh's Centre for Medical Informatics, Chantix isn't any more dangerous from a perspective of cardiovascular risk or depression than Zyban or any nicotine replacement therapy.

The study, which was conducted in England over a period of six months and published in The Lancet Respiratory Medicine, covered 150,000 smokers and tracked their profile in terms of cardiovascular and mental health. What researchers discovered was that there was no statistically significant difference between Chantix users and the rest of the group with regard to adverse cardiovascular events or instances of depression.

In the words of Sheikh:

"Regulators such as the United States Food and Drug Administration (FDA) should review its safety warning in relation to varenicline (the scientific name for Chantix) as this may be unnecessarily limiting access to this effective smoking cessation aid. [It's] highly unlikely that varenicline has any significant adverse effects on cardiac or mental health." 

Understandably, one flaw with the study that can't be overlooked is that while the data pool is enormous, the six-month time frame doesn't give much time to establish a long-term perspective of Chantix's effect on either mental health or a patients' cardiovascular system.

It's not just one study, actually
Then again, this isn't the only recent study that suggests Chantix may be getting a bad rap.

Source: National Institute on Drug Abuse.

In June, a nearly identical study was conducted with the help of 69,757 Swedes and Dr. Seena Fazel, a senior research fellow in the psychiatry department at the University of Oxford in England. Per Fazel's findings, which were published in BMJ, Chantix didn't lead to an increase in suicidal behavior, mental illnesses, or criminal acts. The study did point out that in participants with a history of psychiatric problems, taking Chantix led to a small increased risk of mood changes and anxiety, but otherwise found that the FDA's fears appeared to be overstated.

Another study, released in February of this year and led by Dr. Jon Ebbert, a professor of medicine at the Mayo Clinic in Minnesota, showed that among more than 1,500 patients across 10 countries, Chantix was linked to higher quitting rates among smokers who claimed they weren't ready to quit cold turkey. After a month of the study, 47% of patients taking Chantix reduced the amount they smoked daily by at least half or quit entirely, compared to just 31% of study participants taking the placebo. Further, between the 21st and 52nd week of taking Chantix or the placebo, more than a quarter of the Chantix users completely stopped smoking, compared to just 10% of the placebo patients.

Can Chantix live up to its potential?
Recent study data would seem to suggest that Chantix could be indeed be safer and more effective than the FDA realizes -- but will that change anything?

Source: Flickr user Melanie Tata.

The truth is we just don't know yet. The FDA tends to err on the side of caution when it comes to safety, and with a number of adverse events filed with the agency over more than a half-decade, there are no guarantees the FDA would even consider modifying Chantix's label or giving it another look.

On the flipside, even if Pfizer were to succeed in getting its label modified for Chantix, I'm not entirely certain we'd see a monumental surge in sales. Don't get me wrong, removing or softening the language of Chantix's warnings would likely boost sales of the drug around the world. However, the competitive environment today is a lot different than it used to be. Access to electronic cigarettes, and in some states even legal marijuana, complicates matters, and gives smokers pathways to ease off of their tobacco use without using a prescription therapy.

Nonetheless, I believe this is a developing story worth watching. This could be Chantix's last chance to remove its stigma as a disappointing drug.