The top four pharmacy benefit managers controlled 75% of the national PBM market in 2024, up from 70% in 2022, according to a new analysis from the American Medical Association. The finding sharpens antitrust and regulatory pressure on an industry already facing congressional reform and a proposed Department of Labor transparency rule.

The AMA based its analysis on prescription drug plan and enrollment data from 2022 and 2024, examining market shares of the 10 largest PBMs.

The 2024 ranking reshuffled the industry's upper tier. OptumRx and Express Scripts each held 23% of the national market, CVS Caremark held 18%, and Prime Therapeutics held 11%. In 2022, CVS led with 21%, followed by OptumRx at 21%, Express Scripts at 17%, and Prime Therapeutics at 10%. Express Scripts recorded the largest market share increase between the two periods.

Concentration extends well beyond the national level. The report found that 32 PBM markets, or 94%, were highly concentrated in 2024, compared with 28 markets, or 82%, in 2022.

Vertical Integration Reaches Most Covered Lives

Every one of the 10 PBMs in the report shares ownership with a health insurer. In 2024, 69% of people with commercial or Medicare Part D drug coverage were enrolled with an insurer vertically integrated with a PBM. That integration varies widely across local markets — some show little vertical integration, while others are almost entirely vertically integrated.

The AMA also analyzed national market shares for the 10 largest insurers providing prescription drug benefits. UnitedHealth Group held the largest share in commercial and Medicare Advantage prescription drug plan coverage, while Centene led the stand-alone Medicare Part D market. Kaiser ranked second in the commercial market and Humana ranked second in Medicare Advantage PDP coverage. CVS Health, through Aetna, ranked second in the stand-alone Part D market.

What the AMA Is Saying

"Competitive PBM and prescription drug plan markets help patients get the medications they need at a fair price," AMA President Dr. Willie Underwood III said in a statement. "But our analysis shows that a small number of PBMs account for a growing share of the market, while most local PBM markets remain highly concentrated and most prescription drug benefits are managed by vertically integrated insurers and PBMs."

Underwood called for continued scrutiny. "These trends warrant closer scrutiny, greater transparency and stronger accountability to ensure PBM markets serve patients rather than reinforce the market power of large healthcare companies," he said.

Regulatory and Legislative Backdrop

The report arrives amid an active enforcement and legislative season for the PBM sector. In February, Congress passed reforms including a measure delinking PBM compensation from the price of a drug in Medicare Part D. Separately, a proposed Department of Labor rule seeks to improve transparency in fees and compensation received by PBMs.

The AMA says it hopes to see more efforts to rein in PBMs.

Practical Consequences for Practitioners

For antitrust and healthcare counsel, the AMA's figures supply current market-share evidence that plaintiffs and regulators can deploy in challenges to PBM consolidation and contracting practices. The finding that 94% of local PBM markets are highly concentrated gives litigators a ready benchmark under the Herfindahl-Hirschman-type concentration frameworks the agencies use. The vertical-integration data — 69% of covered lives enrolled with integrated insurer-PBM pairs — will likely feature in future investigations of affiliated-party dealing, steering, and fiduciary-benefit claims under ERISA. Compliance teams at insurers and PBMs should expect the delinking mandate in Medicare Part D and the proposed DOL fee-transparency rule to drive disclosure and rebate-practice overhauls.