It's really quite alarming. The FDA received 4,762 reports of serious psychiatric events since Chantix's 2006 approval. For Zyban and its generic rivals, it received a total 527 reports. And this is where it gets dead serious: It received 98 reports of suicide and 188 reports of attempted suicide with Chantix and 14 reports of suicide and 17 attempts with Zyban and related generics.

So far, the FDA has changed the label on Chantix four times. The FDA, however, stopped short of warning that Chantix is also linked to loss of consciousness, mental confusion, dizziness and muscle spasms.

Pfizer and GlaxoSmithKline will also have to run more clinical trials and are not allowed to advertise the drugs in certain ways. Already, Pfizer has seen Chantix's sales plunge over the last year because of safety concerns. Global sales of Chantix -- $846 million in 2008 -- fell 36 percent in the first-quarter to $177 million.

Since GSK already markets an antidepressant called Wellbutrin with the same ingredient as Zyban and that already carries a warning, it will have to expand it, and Pfizer will have to add one to Chantix. While Pfizer said it will add the warning, it believes the benefits of the drug outweigh the risks.

Indeed, the FDA doesn't want to fully discourage people from using the drugs. "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 in the issued FDA statement. "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."

The key is to know about the risks so patients and doctors can manage them.

Here is the FDA's Public Health Advisory: FDA Requires New Boxed Warnings for the Smoking Cessation Drugs Chantix and Zyban