Pharmaceutical pricing is complicated, but goes something like this: Drug companies like Pfizer (PFE, -3.13%) set the sticker price for their drug. They then negotiate prices on these drugs with insurance companies and vendors, like ExpressScripts (ESRX, -3.20%) that put them in the hands of patients.
http://fortune.com/2016/04/26/drug-prices-valeant-pfizer-merck/