Pharmacy benefit managers (PBMs for short) might be the most important health care companies you’ve never heard of.

So, what is a PBM and how does it impact Rx drug costs?

“Pharmaceutical benefit managers process prescriptions for the groups that pay for drugs, usually insurance companies or corporations, and use their size to negotiate with drug makers and pharmacies,” according to the Wall Street Journal.

One of the country’s largest PBMs is Express Scripts, who reports on its company Web site that, “Employers, unions and government organizations throughout the nation rely on our services. We are in their corner to negotiate with drug manufactures so no one pays more than they need to. Any dollar spent that doesn’t improve health is a dollar wasted.”

A research from from Visante found that PBMs “are projected to save employers, unions, government programs, and consumers $654 billion - up to 30 percent - on drug benefit costs over the next decade.”