From 2000 to 2010, the proportion of U.S. adults with diabetes grew from 6 percent to 9 percent, or nearly 21 million people. But even as the prevalence of this serious and costly condition has risen, the treatment costs borne by patients have actually declined during that period, a new Commonwealth Fund–supported study finds. Writing in the American Journal of Managed Care, researchers Peter Cunningham and Emily Carrier of the Center for Studying Health System Change attribute much of the decline to lower out-of-pocket spending on prescription medications.