Zyban (bupropion) works by diminishing the mental rush or pleasure of cigarette smoking and reducing some of the side effects of withdrawal. It can double the odds of quitting and is an excellent option to help quit.
Unlike chantix, bupropion doesn't actually stimulate the nicotine receptors in the brain. If you're on bupropion, it's a good idea to use a nicotine patch and also a shorter acting nicotine agent like gum, lozenges, the puffer, or the nasal spray. That combination is very effective at helping even severely addicted people quit tobacco.