Chantrix (varenicline) is a new drug for quitting smoking -- just approved earlier this year.
It works differently from other quit-smoking drugs like Zyban. It mimics the effect of nicotine by binding with nicotinic receptors in the brain. By this means it reduces cravings and withdrawal symptoms. Because the drug blocks the nicotine receptors, it may also lessen the pleasure people get from nicotine use. Essentially the drug "gets there first," so that the real nicotine can't bind to the receptors.
It has some possible side effects, at least in some people, including nausea, headache, and trouble sleeping. Some people taking Chantrix report that it caused them to have weird dreams.
I don't know if the FAA has yet evaluated Chantrix, or if they have, how they have ruled on the drug.
Here's a link to an article about the clinical trials with Chantrix:
Varenicline helps more smokers quit longer with fewer side effects - National Cancer Institute
In truth, the main ingredient in quitting smoking is DESIRE. If you really, really, really want to quit, you will, with or without any of the various quit-smoking aids. (Ex-smoker here -- finally quit in 1989 when I ran out of excuses to continue my 2-pack a day habit!

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