Many know UnitedHealth Group (NYSE:UNH) as the largest health insurance provider in the U.S., but you may not know it as the nation's third largest pharmacy benefit manager, or PBM, after Express Scripts (NASDAQ:ESRX) -- which recently acquired Medco -- and CVS Caremark (NYSE:CVS). In recent years, Medco has managed the pharmacy benefits for UnitedHealth's commercial customers, but UnitedHealth is ending that relationship and bringing all PBM services in-house. This cost-cutting move by UnitedHealth should save the company hundreds of millions of dollars, but represents the loss of a huge customer for Express Scripts. Is this move part of a larger trend of companies cutting costs by bringing PBM services in-house? That could have major implications for investors, as Motley Fool analyst Brenton Flynn outlines in the video below.