The Government Accountability Office verified both drug makers’ assertions that the amount of rebates they pay is rising much faster than drug net prices and pharmacy benefit managers’ assertion that they pass nearly all rebates to their insurer clients. Pharmacy benefit managers primarily earned Part D revenue from either the volume-based fees or per-member, per-month fees that insurers pay them. The drug-channel middlemen kept less than 1% of the rebates they negotiated. The rest was passed to insurers. Insurers use...