Chantix — the generic name is varenicline — is a relatively new medication used to help smokers quit. Although it has been shown to be helpful when used in a comprehensive smoke-ending program, this drug is now known to cause psychiatric symptoms, such as depressed mood, agitation, and changes in behavior, as well as suicidal thoughts and attempts.

The U.S. Food and Drug Administration (FDA) has issued a series of alerts on this issue. Read the latest from the FDA.

One case reported sounds similar to what you describe: A patient with a history of depression, who had done well on an antidepressant, became depressed after she started varenicline, despite continuing her antidepressant.

There is not much information available about interactions between varenicline and antidepressants. So what you have observed is quite possible. At this point, the best we can say is that varenicline may be suppressing your mood; in effect, it is counteracting the positive results you've gotten from your antidepressant.

Remember that mood can change because of nicotine withdrawal. Depressed mood and anxiety are pretty common consequences of quitting smoking. Or the change may be coincidental, a downswing that may have occurred with or without varenicline.

Congratulations on taking the very positive step toward quitting cigarettes to improve your health. And it's also positive that you are aware of your mood change. Depression can be dangerous to your health, too.

A short vacation from the varenicline may move your mood back to what feels normal to you. Such a test might give you enough information to judge the merits of continuing varenicline treatment.

Please keep your doctor involved in the discussion, because he or she is in the best position to help you sort out these questions and can offer treatment and support if your mood declines further.