This research examines the effects of causal beliefs on drug preference. In three studies, 374 undergraduate participants imagined that they suffered from a focal symptom and then indicated their preference between a drug claiming to treat only the focal symptom (single treatment) and a drug claiming to treat the focal symptom and a nonfocal symptom (dual treatment) they thought resulted from a common‐cause or from a different cause. Participants who thought that the symptoms resulted from different causes significantly preferred the single treatment drug more and the dual treatment drug less than participants who thought the symptoms resulted from a common‐cause. Process analysis yielded a significant mediation effect. Specifically, an individual's causal model determines preference by affecting the estimates of the potential gain and loss associated with using each drug. Participants who held a common‐cause model concerning the source of the symptoms thought they would be more likely to need the nonfocal treatment provided by the dual treatment drug and less likely to suffer from side effects when taking this drug, than those with a different‐cause model. The results demonstrate the influence of causal structure on judgment and choice. © 2017 The Authors Journal of Behavioral Decision Making Published by John Wiley & Sons Ltd.