New Challenge for Medco

"The PBMs could see their total revenue go down," Garis says. "So their balance sheets would look much worse on that side. ... But what I think will happen in reality -- and even the analysts mention this -- is that the PBMs will just make up for this with extra markups on the generic side of the business."

Still, Wal-Mart could dampen those plans.

Notably, the heavyweight retailer has started selling 30-day supplies of certain generic drugs for just $4 apiece.

To be fair, Wal-Mart has included just a fraction of all generic drugs on its $4 list. However, Garis feels, the company has made an important statement in the process.

"Wal-Mart has said with its actions, 'Look, guys, generics shouldn't be that expensive,'" Garis states. "And, in fact, they aren't. Wal-Mart is going to at least break even on this promotion."

Giant employers and health plans, who rely on PBMs to secure the cheapest drug prices possible, could take notice and demand low-priced generics for themselves.

Garis, for one, hopes they do. If that happens, he says, those clients could see their total drug costs actually go down -- reversing an expensive trend -- a few years down the road.

That said, he still questions whether PBMs will suffer in the process.

"I think the PBMs will have to find another place to generate their big cash flows," Garis says. "And they always do. As much as I hate to admit it, they have made strategic moves that look very, very astute. They've always managed to stay ahead of the ballgame."

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