“The current administration is particularly focused on bringing down prescription drug prices for consumers and has specifically targeted PBMs as the part of the supply chain that is overearning relative to the value they produce,” Icahn wrote in his letter.

“There is a strongly held belief that the rebate system, which Express Scripts relies on heavily, is a rigged game with conflicting incentives that might actually be pushing up drug prices. The recent proposed rule to remove the safe harbor protection for rebate payments is a clear shot across
the bow for the PBM industry and occurred after the signing of the Cigna/Express Scripts merger agreement.”

More at: https://www.forbes.com/sites/brucejapsen/2018/08/07/icahn-opposes-cigna-express-scripts-deal-citing-amazon-and-flawed-rebates/