PBMs play a key role in the prescription drug market in the United States. They are hired by health plans, employers, and prescription benefit plans to negotiate with pharmaceutical manufacturers, who then provide discounts, called rebates, on their medications. While PBM clients now receive the majority of rebates and make benefit design and payment model decisions, the role of PBMs has also grown in importance over recent years as drug spend has accelerated. According to the NIH, overall pharmaceutical expenditures in the United States grew 13.6% from 2022 to 2023, for a total of $722.5 billion.¹ And the three largest PBMs (Caremark, Express Scripts, Optum Rx) processed nearly 80% of the approximately 6.6 billion prescriptions dispensed by U.S. pharmacies in 2023.²