Common Agent or Double Agent? Pharmacy Benefit Managers in the Prescription Drug Market

In the U.S., pharmacy benefit managers (PBMs) manage prescription drug purchases for payers. Firms selling branded pharmaceuticals bid for preferred slots on the PBM's formulary by offering rebates off of list price. We find that PBMs enhance efficiency, but the gains do not accrue to consumers or drug makers. Our analysis offers insights into otherwise puzzling questions. Why do drug makers pay rebates to PBMs? Why do payers delegate formulary operations to a few large PBMs? Why are list prices so high? Why might PBMs vertically integrate with payers? Our framework also offers insights into proposals for market reform.