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

The Federal Trade Commission on Friday filed a lawsuit over insulin prices against the three largest pharmaceutical middlemen that negotiate prescription drug prices, arguing that the companies artificially inflate the costs of the lifesaving diabetes drug for patients.

Three companies that process about 80% of prescriptions in the United States — Caremark, Express Scripts and OptumRx — have engaged in anticompetitive practices that spur price increases, the