A September 2026 American Medical Association Policy Research Perspective analyzed Decision Resources Group data on PBM and insurer market shares from 2022 to 2024. Together, the four largest PBMs controlled 75% of the national market, up from 70% in 2022.
Here are six things to know:
- OptumRx was the largest PBM by rebate-negotiation market share in 2024 at 23%, followed closely by CVS Caremark at 18% and Prime Therapeutics at 11%.
- Local PBM markets were even more concentrated: The average Herfindahl-Hirschman Index across PDP regions rose 164 points to 2,574, and the share of highly concentrated local markets climbed from 82% to 94%.
- The study found extensive vertical integration between insurers and PBMs: 69% of PDP lives nationally were covered by an insurer vertically integrated with a PBM, ranging from 67% of commercial PDP lives to 77% of Medicare Advantage PDP lives.
- UnitedHealth Group was the largest PDP insurer nationally in both commercial and Medicare Advantage PDP markets.
- The AMA said high concentration and vertical integration raise antitrust concerns, since PBMs may not fully pass rebate savings through to consumers and nonintegrated insurers may face higher costs or reduced access to competitive PBM rates.
- The findings extend a running series of AMA reports tracking PBM consolidation. A prior report found the top four PBMs controlled 70% of the national market as of 2022. The findings also echo FTC scrutiny of the same dynamics. The agency’s second interim report found the three largest PBMs generated more than $7.3 billion in excess revenue by marking up specialty generic drugs between 2017 and 2022. A separate HHS Office of Inspector General analysis published this year also found enrollees in vertically integrated Part D plans paid nearly 40% more in out-of-pocket drug costs than those in nonintegrated plans, despite similar overall net costs.
