Bupropion, a prescription antidepressant marketed as Zyban®, was approved by the FDA in 1997 to treat nicotine addiction. This drug can help to reduce nicotine withdrawal symptoms and the urge to smoke, and can be used safely with nicotine replacement products. Some common side effects of bupropion are dry mouth, difficulty sleeping, headache, dizziness, and skin rash. People should not use this drug if they have a seizure condition such as epilepsy or an eating disorder such as anorexia nervosa or bulimia, or if they are taking other medicines that contain bupropion hydrochloride. Also, people should avoid using alcohol while taking buproprion because alcohol consumption increases the risk of having a seizure.
Varenicline, a prescription medicine marketed as Chantix™, was approved by the FDA in 2006 to help cigarette smokers stop smoking. This drug may help those who wish to quit by easing their withdrawal symptoms and by blocking the effects of nicotine from cigarettes if they resume smoking. Some common side effects of varenicline are nausea, changes in dreaming, constipation, gas, and vomiting. People should not use this drug if they have kidney problems, and women should not use this drug if they are pregnant, plan to become pregnant, or are breastfeeding.
Although nortriptyline and clonidine are not currently approved by the FDA for the treatment of nicotine addiction, doctors sometimes prescribe these drugs to help people quit smoking.
This answer is based on source information from the National Cancer Institute.