Although it has relatively mild binding affinities for dopamine and norepinephrine reuptake pumps (at usually prescribed doses), bupropion is postulated to have its antidepressant effect through the antagonism of these pumps. Binding at other sites is even lower. Bupropion’s side effects of tremors and sweating are consistent with increased levels of dopamine and norepinephrine.

It appears, therefore, that bupropion’s metabolites play a role in its pharmacologic activity. Bupropion has several active metabolites, and their clearance is slower. The total concentration of bupropion with its metabolites likely accounts for the overall effect of increasing dopamine and norepinephrine.

With information from: Bupropion: What Mechanism of Action? Sheldon H Preskorn, MD. Journal of Practical Psychiatry and Behavioral Health, January 2000, 272-276.