July 1, 2009 -- The FDA warns that bizarre behavior -- including suicide -- is seen in people taking the stop-smoking drugs Chantix and Zyban.

Both drugs now will carry "black box" labels warning that people taking the drugs should be closely watched for signs of suicidal thoughts, depression, hostility, or other changes in behavior.

"We want people to use these drugs carefully and pay attention," Robert J. Temple, MD, director of the FDA's office of medical policy, said at a news conference. "Stopping smoking is a goal we all want to work toward. We don't want to scare people off these drugs -- we just want them carefully monitored."

It's not at all clear that the drugs actually cause these behavior changes. Smokers are addicted to nicotine -- and when they quit, their withdrawal symptoms can include many bizarre behaviors, including suicide.

However, Curt Rosebraugh, MD, MPH, director of one of the FDA's drug evaluation units, said that some of the suicide reports came from Chantix users who were still smoking.

The FDA has been following reports of suicide and bizarre behavior in people taking Chantix. Indeed, the FAA bans use of the drug by pilots, and the FDA warns people not to operate heavy machinery while using the drug. But the link between such behaviors and Zyban is relatively new.

Zyban's active ingredient is bupropion, the antidepressant medication sold as Wellbutrin. While Wellbutrin and other antidepressants have labels warning of suicidal thoughts, the warning had not been fully extended to people taking Zyban to quit smoking.

"Our attention was focused on Chantix. It wasn't until we started looking through things that we realized Zyban may have the same issues," Rosebraugh said at the news conference.

The most disturbing reports to the FDA involve suicide:

98 completed suicides in Chantix users

14 completed suicides in Zyban users

188 attempted suicides in Chantix users

17 attempted suicides in Zyban users

These reports have not been fully investigated. There may be duplicate reports, and the reports have not been definitively shown to be drug side effects.