If you tuned into this past week’s Democratic presidential debates you got an earful on runaway health costs and various proposals to solve the health-care access problem. But amid the talk of Medicare for All, universal care, a public option, and other bold proposals, one underlying issue continues to dominate the discussion inside and outside of Washington: The high-cost of pharmaceutical drugs.

A recent analysis by Kaiser Family Foundation adds new light on exactly who bears the brunt of these costs and why.

Just 5% of all Americans account for at least 50% of health-care spending, according to the Kaiser study. That makes sense. Of course the sickest people spend the most on health care.

But what may be more surprising is the fact that prescription drugs account for an astounding 40% of spending among high-cost patients, pointing out once again how disproportionate the cost of prescription drugs can be, said Drew Altman, CEO and President of Kaiser Family Foundation.

“A very small group of patients with major illnesses is responsible for an outsized share of health-care spending,” Altman writes in a recent column for Axios. This new research shows that prescription drugs are a big part of the reason their bills are so high.