Varenicline
"Four weeks on Chantix worked.  I stopped taking the drug a week ago and still don't have the desire to smoke.  I definitely experienced nausea and have had the worst sleep of my life over the last month.  I had a hard time falling asleep and an even harder time staying asleep.  Another side effect has been weight gain.  Over the course of the last 18 years I've gained 25 pounds, and 15 of that 25 has been in the last 4 weeks!  Lastly, I (and those around me) have noticed that I'm extremely irritable and aggressive.  In my first couple of days off the meds I felt depression like I never have and was even more irritable.  The weight gain still continues."