"PBMs serve as the 'middlemen' in most prescription drug transactions in the United States. First, they leverage the number of beneficiaries in a plan to negotiate lucrative rebates from pharmaceutical manufacturers. Second, they formulate limited pharmacy provider networks that will supply or dispense these drugs to plans' beneficiaries and in turn, charge plan sponsors for these products.... PBMs extract 'spread' profits from both activities. Unless a plan has negotiated a true 'pass through' contract with its PBM -- and typically only the largest and most sophisticated plans are able to do so -- the PBM will keep a significant percentage of the rebate dollars that they have obtained only by virtue of the number of the plans' beneficiaries for themselves."  MORE >>