A study conducted by Qato et al. (2024) examines the level of market concentration within the pharmacy benefit manager (PBM) industry.
Overall, the PBM market showed significant concentration, with an HHI [Herfindahl Hirschman Index] of 1972. The lowest HHI was observed in commercial insurance at 1940, with 90 PBM participants, while the highest was in Medicare Part D at 2399, with 21 PBM participants.
The majority of market share is held by three major PBMs. CVS Caremark, Optum Rx, and Express Scripts collectively fill 73.6% of retail prescriptions, although this varies across different payer types.
For example, CVS Caremark dominates in the Medicaid managed care market with a share of 39.2%, while Express Scripts holds 28.0% of the commercial market. Optum Rx and SS&C Health have a larger presence in the Medicare Part D market compared to other markets.

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