Four PBMs Now Manage 75 Percent of the Market, an AMA Report Finds. It Shows Concentration, Not Prices.
The AMA's September analysis finds 94 percent of local PBM markets highly concentrated, up from 82 percent in 2022. The study is descriptive and comes from a physician advocacy group; the practical stake is in your prior authorization workload.
The four largest pharmacy benefit managers (PBMs) managed 75 percent of the national market for rebate negotiation in 2024, up from 70 percent in 2022, according to an American Medical Association analysis. In 94 percent of local markets, concentration is high enough to meet the standard definition of "highly concentrated." In 2022 that figure was 82 percent.
The report, a Policy Research Perspective dated September 2026 by AMA economics director José R. Guardado, PhD, was released Oct. 2, according to the AMA's advocacy update, and summarized by the AMA on Oct. 8. It matters to practices because PBMs set the formularies, step therapy and prior authorization rules that land in your inbox.
What the AMA's analysis found
Measured by rebate negotiation, OptumRx held a 23 percent share in 2024, with Express Scripts a close second at 23 percent, CVS/Caremark at 18 percent and Prime Therapeutics at 11 percent. Local concentration is measured with the Herfindahl-Hirschman Index (HHI), where a score above 1,800 is highly concentrated. The average across prescription drug plan regions was 2,574, up 164 points from 2022.
The report also measures vertical integration between insurers and PBMs. Nationally, 69 percent of prescription drug plan lives are covered by an insurer integrated with a PBM. The share is 73 percent in Medicare Part D, 77 percent in Medicare Advantage drug plans and 67 percent in standalone Part D plans. The AMA says each of the 10 largest PBMs shares ownership with a health insurer.
Concentration is a measure of market structure. It is not evidence about prices, and the report says so.
What the report does not show
The analysis is descriptive. The author writes that integration can lower costs by removing a second markup, and that the effect on consumers is ambiguous, although the limited empirical work so far is more consistent with harm. It cites a study of a 2015 insurer-PBM merger in which non-integrated insurers saw premium increases. On whether concentration raises prices, premiums or keeps rebates from being passed through, the report says, "Empirical evidence is needed to shed light on these questions."
Readers should also keep in mind who published it. The AMA is an advocacy organization with a stated position on PBM regulation. The data come from Decision Resources Group, and commercial figures omit about 39 percent of commercial lives, whose drug benefit is carved out of the health plan. Medicare Part D lives are not affected by that gap.
The policy backdrop
The report notes that this year's Consolidated Appropriations Act places limits on PBM compensation in Medicare Part D and requires that rebates be fully passed through, and that Congress reintroduced the Patients Before Monopolies Act, which would bar common ownership of PBMs and pharmacies. Neither is described as having changed market shares. Drug pricing is moving on several fronts, including Medicare's Part B model; see our coverage of the GLOBE model.
What it means in clinic
For a practice, the number to track is how often PBM rules delay or change treatment. Ask your staff to log prior authorization requests, step-therapy exceptions and formulary switches by PBM for a month. That log is the data you will need if you submit comments, appeal to a plan or join your state society's advocacy on PBM bills.
Reported, fact-checked and edited by The Script Pad's editorial staff.
This article is for professional education and does not replace clinical judgment. Treatment decisions should be based on the individual patient and current guidelines.
