Pharmacy benefit managers (PBMs) play an important role in financing and delivering prescription drugs for health insurers, including designing formularies and pharmacy networks, negotiating drug prices, and reimbursing pharmacies.1 Despite evidence that 3 PBMs (CVS Caremark, Express Scripts, and Optum Rx) accounted for 79% of prescriptions in the US in 20232 and growing concerns about the role of the highly concentrated PBM market on rising out-of-pocket costs and pharmacy closures,3,4...