Pfizer, GSK's stop-smoking meds get warning

Federal regulators have ordered new safety language on the smoking cessation drugs Chantix (varenicline) and Zyban (buproprion). The two meds are getting the toughest warning added to their labels, alerting doctors and patients to potentially severe mental health risks, including behavioral changes, depression, hostility, suicide, and suicidal thoughts, as well as warnings about allergic and skin reactions.

The FDA has been reviewing Chantix safety since 2007, after hundreds of reports of erratic, aggressive and suicidal behavior. But as the agency notes, it's difficult to confirm these drugs are directly responsible, because nicotine withdrawal itself can be very difficult to endure. There's also the possibility that Chantix exacerbates symptoms of underlying mental illness rather than causing them--a problem that would have gone undetected in clinical trials because they excluded patients with a history of mental illness.

Hence the new trials FDA is requiring both Pfizer and GlaxoSmithKline, Zyban's maker, to undertake. Pfizer says it's currently conducting a safety study involving patients with schizophrenia and is in talks with the FDA regarding comparative studies. Glaxo will also be required to study Zyban's mental health effects on patients, including those with pre-existing mental problems.

"The risk of serious adverse events while taking these products must be weighed against the significant health benefits of quitting smoking," said Janet Woodcock, M.D., director, the FDA's Center for Drug Evaluation and Research. "Smoking is the leading cause of preventable disease, disability, and death in the United States and we know these products are effective aids in helping people quit."

Pfizer won't yet say how the warning might affect its financial forecast or its Chantix sales force, but promises an update July 22 on sales figures for its primary care unit, in tandem with its earnings report. Meanwhile, GSK hasn't released a statement at all, despite the fact that the warning goes onto two of its meds: Zyban is sold as an antidepressant under the brand name Wellbutrin, and that drug gets updated "boxed warning" language added to its current "boxed warning" of suicidal thoughts and behavior. Generic versions, too. But Glaxo doesn't make much off Zyban, while Chantix is one of Pfizer's top selling meds, bringing in $846 million last year. 

- read the FDA announcement
- here's Pfizer's response
- get more from CNBC
- check out the story in the New York Times