The Federal Trade Commission's administrative complaint follows an interim report from the agency regarding PBM practices.

The FTC said CVS Caremark, Cigna’s Express Scripts, and UnitedHealth’s OptumRx profit at the expense of patients forced to pay more for insulin.

The U.S. Federal Trade Commission sued the country's three largest pharmacy benefit managers on Friday, accusing them of steering diabetic patients towards higher priced insulin in order to reap millions of dollars in rebates from pharmaceutical companies.

Pharmacy benefit manager Express Scripts sued the U.S. Federal Trade Commission on Tuesday over the regulator's recent drug pricing report, calling the report's conclusion that the prescription middlemen raise drug costs defamatory.

At issue is a report released by the FTC in July called: “Pharmacy Benefit Managers: The Powerful Middlemen Inflating Drug Costs and Squeezing Main Street Pharmacies.” Express Scripts claims in the lawsuit that the report “is seventy-four pages of unsupported innuendo” leveled against it and other PBMs.

The FTC suit targets the three biggest so-called pharmacy benefit managers, UnitedHealth Group's Optum Rx, CVS Health's Caremark and Cigna's Express Scripts.