I examine physician agency in health care services in the context of the choice between brand-name and generic pharmaceuticals. I examine micro-panel data from Japan, where physicians can legally make profits by prescribing and dispensing drugs. The results indicate that physicians often fail to internalize patient costs, explaining why cheaper generics are infrequently adopted. Doctors respond to markup differentials between the two versions, indicating another agency problem. However, generics’ markup advantages are short-lived, which limits their impact on increasing generic adoption. Additionally, state dependence and heterogeneous doctor preferences affected generics' adoption. Policy makers can target these factors to improve static efficiency.

This study tests whether demand responds symmetrically to price increases and decreases—a seemingly obvious proposition under conventional demand theory that has not been rigorously tested. Exploiting the rapid expansion in Japanese municipal subsidies for child health care in a difference-in-differences framework, we find evidence against conventional demand theory: when coinsurance, our price measure, increases from 0% to 30%, the demand response is more than twice that to a price decrease from 30% to 0%. This result indicates that while economists and policymakers pay little attention, price change direction matters and should be incorporated into welfare analysis.