If you're one of the 45 million adults who smoke, trying to quit can be a daunting task. Using medication, like Chantix, increases the chance of quitting successfully, according to the American Lung Association. However, Dr. Steven Schroeder, director of the University of California, San Francisco Smoking Cessation Leadership Center, says the prescription drug isn't for everyone.

"If a consumer has a history of suicidal thoughts, severe depression or bipolar disorder, Chantix is not a good choice of medicines to stop smoking," he says. "If suicidal thoughts occur in a person using Chantix, they should discontinue the medication and seek professional help immediately."

Chantix takes the pleasure out of smoking by interfering with the way nicotine ordinarily affects the brain. At the same time, it spurs the release of dopamine, which helps control the brain's pleasure centers.

Pfizer, the makers of Chantix, caution some people have experienced hostility, agitation, depressed mood, nausea and problems sleeping while taking the drug, but add that quitting cold turkey can also cause side effects. "Quitting smoking, with or without Chantix, may be associated with nicotine withdrawal symptoms, including psychiatric symptoms, such as depression," says company spokesman MacKay Jimeson. "Smoking is a major public health issue - it's the leading cause of premature death in the United States. The health benefits of quitting smoking are immediate and substantial."