The Federal Trade Commission took action Friday against the three largest pharmacy benefit managers, accusing the companies of “engaging in anticompetitive and unfair rebating practices that have artificially inflated the list price of insulin drugs,

The US Federal Trade Commission sued units of CVS Health Corp., Cigna Group and UnitedHealth Group Inc. on Friday, accusing the drug middlemen of engaging in illegal rebate programs that drove up the price of insulin.

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.

Months earlier, the agency released a report alleging the companies drove up the costs of some medications, including insulin.

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

Insulin, used by millions of Americans, has taken center stage in the high-stakes battle over health care costs. Though prescribed for the past 100 years, only three companies supply insulin in the U.S. and much of that is higher-cost branded versions, despite the increasing availability of lower-price biologic options.

The agency alleges CVS’s Caremark, Cigna’s Express Scripts and UnitedHealth’s Optum Rx accepted money from drugmakers in exchange for keeping lower-cost insulin off their lists.

The Federal Trade Commission sued the drug middlemen that health plans use to keep a lid on drug spending, accusing the firms of inflating the price of insulin.