Bupropion non-competitively blocked function of 5-HT3ARs in X. laevis oocytes. Bupropion inhibition at these receptors was non-use-dependent. The metabolite hydroxybupropion also inhibited function of 5-HT3ARs in oocytes. Our study establishes the 5-HT3AR as a hitherto unidentified molecular target of bupropion. The study further provides a novel pharmacological basis for bupropion's antidepressant effect.