%S TSE Working Paper %A Helmuth Cremer %A Jean-Marie Lozachmeur %T Coinsurance vs. copayments : reimbursement rules for a monopolistic medical product with competitive health insurers %X This paper studies a market for a medical product in which there is perfect competition among health insurers, while the good is sold by a monopolist. Individuals diĀ¤er in their severity of illness and there is ex post moral hazard. We consider two regimes : one in which insurers use coinsurance rates (ad valorem reimbursements) and one in which insurers use copayments (specic reimbursements). We show that the induced equilibrium with copayments involves a lower producer price and a higher level of wel- fare for consumers. This results provides strong support for a reference price based reimbursement policy. %K Ex post moral hazard %K health insurance competition %K copayments %K imper- %K fect competition %B TSE Working Paper %V 21-1223 %D 2021 %C Toulouse, France %I TSE Working Paper %L publications43614