Dopaminergic transmission in the central nervous system is thought to underlie addictive behaviours, including smoking. One effective smoking cessation drug, bupropion, enhances dopaminergic transmission; conversely, antipsychotic drugs, which are dopamine antagonists, are associated with increased smoking. Thus we hypothesized that subfertile women treated with the potent dopamine agonist bromocriptine might smoke less as a consequence of their treatment. Among 4,608 subfertile women those conceiving on bromocriptine were half as likely to smoke as those taking other drugs or those conceiving without medication (p < 0.0001). This observation supports the role of dopamine in nicotine addiction, and suggests that bromocriptine-like drugs could be used effectively by pregnant women to aid cessation.