This study shows how consumers’ brand preferences are related to professional experts’ behavior by investigating the role of pharmacists. Although the literature suggests that consumers are more willing to pay for brand-name products, our data reveal a puzzling scenario: some patients continue to choose nonbrand generic alternatives even when a brand-identical option (authorized generic) is available at the same price. We model both patients’ demand and pharmacies’ drug adoption decisions and demonstrate substantial variation in brand preferences across pharmacies using Japanese pharmacists’ dispensing data. Furthermore, our results indicate that differences in pharmacists’ medical management are important in shaping these preferences.