This econtalk episode[1] provides some interesting background on how this happens with medication. There are man-in-the-middle companies (Pharmacy Benefit Managers - PBM) that negotiate plans with pharma companies. These companies get paid a commission based on the delta between list price and the deal they got. The Pharma companies need these deals, so both benefit by the pharma company increasing list prices every year and then cutting better deals to those PBMs. If someone is offering a generic that's cheaper, there is less incentive for PBMs to add them to their plan, because the prices are too cheap to begin with and they have a smaller market share initially. It's all a giant Rube Goldberg machine of a mess.

EDIT: One more interesting detail from the podcast and the book it's based on: Those deals between PBMs and pharma companies are secret. Not even the insurance companies know the details of what's in there.

It's also fun to point out that typically this is everyone involved in a consumer getting their drug: * the consumer * the consumer's employer who selects the insurance * the insurance * a PBM who get a Pharma benefit plan for the insurance * the Pharma company that manufactures the drug * the pharmacy you actually buy the drugs. On top of that the actual payment apparently happens often months after you received the drug.

Edit2: Clarifying "PBM"

[1]http://www.econtalk.org/robin-feldman-on-drugs-money-and-sec...