Of greater importance than the additional retail pharmacy share is Rite Aid's pharmacy benefits manager (PBM), Envision Pharmaceuticals. PBMs are a critical piece of the healthcare delivery system, carrying extra negotiating and administration weight between drug manufacturers and retailers. CVS acquired its PBM in 2007 with the Caremark acquisition and now Walgreens will have one as well.

Medical costs will continue to be a hot-button issue in Washington, and drug pricing will likely face downward pressure. Walgreens should be able to use its integrated delivery network and massive size to pass much of that pressure on to the drug manufacturers, keeping its own margins intact.

The merger, still subject to regulatory scrutiny, puts Walgreens' $3 billion repurchase program on hold and the combination may take a few quarters to fully integrate, but it will further position Walgreens as a power in the growing healthcare system.