You don't have to look far these days to find stories about the rising costs of prescription drugs. By one count, drug spending jumped 13 percent last year, the highest annual increase in more than a decade. And health insurers have spent the better part of the past year warning anyone who'll listen that the new medications will come with high price tags that will strain the health-care system's ability to afford such medical advances.

That adds important context to news this morning that UnitedHealth Group has dropped $12 billion on Catamaran, a pharmacy benefits manager that negotiates with drugmakers and pharmacies to secure better deals on behalf of clients. Catamaran adds to UnitedHealth's drug benefits division, and the acquisition creates what will be the country's third-largest pharmacy benefits manager (or PBM) behind Express Scripts and CVS Health, according to Bloomberg.

The acquisition gives UnitedHealth, the largest U.S. health insurer, more negotiating power as health insurers continue to put public pressure on how drugmakers price their products. The most notable example recently has been the pricing of three new hepatitis C medications, which represent vast improvements over previous drugs but cost at least $84,000. As a ProPublica/Washington Post story revealed Monday morning, Medicare spent $4.5 billion on new hepatitis C drugs in 2014 — more than 15 times what the seniors' health-care program paid the previous year on treatments for liver disease.

Medicare isn't allowed to negotiate directly with drugmakers, but the PBMs can. And as new competing hepatitis C treatments hit the market late last year, these PBMs scored exclusive deals with drugmakers to offer their products. They negotiated undisclosed discounts while also promising a wider swath of patients could receive the treatments.

Express Scripts, the nation's largest PBM, has said it hopes to exert similar pressure on drugmakers for new drugs expected to hit the market for complex conditions including cancer, multiple sclerosis and rheumatoid arthritis. CVS signaled last month it would pressure pharmaceutical companies on pricing for a new wave of cholesterol drugs. Potentially millions of patients could benefit from these new cholesterol treatments, which are expected to cost anywhere between $7,000 and $12,000, CVS officials wrote in the Health Affairs policy journal.

UnitedHealth's purchase of Catamaran also comes just six weeks after Rite Aid beefed up its PBM business with a $2 billion acquisition of its own. The typical consumer may not know what PBMs are, but they could soon become a much greater force in the health care that they receive.