Generic Zyban contains Bupropion as active ingredient which belongs to the pharmacological class of anti-depressants. Bupropion is an atypical antidepressant chemically similar to diethylpropion, an appetite suppressant. The mechanism of the antidepressant effect of bupropion is not completely known, but bupropion inhibits reuptake of dopamine, noradrenaline, and serotonin in the central nervous system, is a non-competitive nicotine receptor antagonist, and at high levels constraints the firing of noradrenergic neurons in the locus ceruleus.
It is not clear which of these effects accounts for the antismoking activity of the drug, but inhibition of the reductions in levels of dopamine and noradrenaline levels in the central nervous system that occur in nicotine withdrawal is might be crucial. The antismoking effect of bupropion is not related to the antidepressant effect.