Explaining why increases in generic use outpace decreases in brand name medicine use in multisource markets and the role of regulation

Background: Healthcare systems worldwide face escalating pharmaceutical expenditures despite interventions targeting pricing and generic substitution. Existing studies often overlook unwarranted volume increases in multisource markets due to differential physician perceptions of brand name and generics. Objective: This study aims to explain the outpacing of generic medicine use over brand name use in multisource markets and assess the regulatory role, specifically examining the impact of reference pricing on volume and intensity increases. Methods: Analyzing German multisource prescription medicine markets from 2011 to 2014, we evaluate regulatory mechanisms and explore whether brand name and generic medicines constitute separate market segments. Using an Oaxaca-Blinder decomposition approach, we divide the differential in brand name versus generic medicine use rates into market structure and unobserved segment effects. Results: Generic use rates surpass same-market brand name substitution by 3.87 prescriptions per physician and medicine, on average. Reference pricing mitigated volume increase, treatment intensity and expenditure. Disparities in quantity and expenditure dynamics between brand name and generic segments are partially explained by market structure and segment effects. Conclusion: Generic medicine use effectively reduces expenditures but contributes to increased net prescription rates. Reference pricing may control medicine use, but divergent physician perceptions of brand name and generics, revealed by identified segment effects, call for nuanced policy interventions.