Quitting or Stopping Smoking with Zyban
Zyban is a drug marketed by Glaxo-Wellcome and has been used, very successfully, to treat nicotine addiction directly. In this case it is different to the way other anti-smoking agents work, such as nicotine gum and patches, since these simply supply an alternative source of nicotine other than cigarettes. Zyban works at the neurological level, reducing the craving for nicotine in any form. At the moment it is licensed in the US, but not yet in the UK. It is potentially
extremely important, as this discovery could open the door to finding similar molecules for treating much more serious addiction problems, such as cocaine and heroin, etc.
There are apparently two reasons to believe antidepressants and anxiolytics might help in smoking. First, anxiety and depression are symptoms of nicotine withdrawal, and smoking cessation sometimes precipitates depression. Second, smoking appears to be due, in part, to deficits in dopamine, serotonin and noradrenaline, all of which are increased by anxiolytics and antidepressants.

The active ingredient in Zyban, like Wellbutrin, is bupropion, a relatively weak inhibitor of the neuronal uptake of dopamine, serotonin and norepinephrine. Chemically, bupropion is related to phenylethylamines and has a relative molecular weight of 276.2. Although, bupropion was initially marketed as an anti-depressant (Wellbutrin), it is chemically unrelated to tricyclic, tetracyclic, selective serotonin reuptake inhibitors or other known anti-depressants.

Warnings, Cautions and Various Nasty Possibilities
Insomnia and dry mouth are the most common side effects associated with this medication. However, there are certain medical conditions which warrant against using bupropion. These conditions include seizures, eating disorders, and current use of certain other medications, such as Wellbutrin. Of course, you should always check with your physician prior to starting any medication, and you should be monitored regularly during treatment.
Using Bupropion
Treatment with bupropion begins while the user is still smoking, one week prior to the quit date. Treatment is then continued for 7 to 12 weeks. Length of treatment should be based on the relative benefits and risks for each individual, and should be discussed with a physician. People who have not made significant progress towards abstinence by the seventh week of therapy are unlikely to successfully quit during this attempt, and bupropion treatment should be discontinued. Dose tapering is not required when discontinuing treatment.
The effectiveness of Zyban for Smoking Cessation here.
Information about Zyban as an aid in beating Nicotine Addiction here.
Quitnet bupropion medication guide here.