Insurance companies get all the attention for gatekeeping Americans’ health care. But another corporate middleman may have even more influence over prescription prices: pharmacy benefit managers, or PBMs. Most Americans haven’t heard of them, and that invisibility is part of their power.

Senate candidate Abdul El-Sayed explained the role of PBMs to Jacobin. They “sit in the middle of a four-way transaction that happens every day in health care, between a patient, a health insurance company, a pharmaceutical manufacturer, and a pharmacy,” El-Sayed said. “And because they sit in the four-way transaction, they are well-poised to be able to pick everyone’s pocket.”

A PBM is hired by the payer — an insurance company, employer, or union — to act as an administrator for its prescription benefit accounts. As an administrator, PBMs are responsible for designing and managing formularies on behalf of the payer, an obfuscating term for the master list of your prescription benefits. They determine which medications insurance will cover, which are preferred, which require prior authorization or step therapy, which pharmacies are in-network and the copays, deductibles, and coinsurance. They handle negotiations with drug manufacturers and process pharmacy claims.