One in seven Americans under age 65 went without prescribed medicines in 2007 as drug costs spiraled upward in the United States, a nonprofit research group said on Thursday.

That figure is up substantially since 2003, when one in 10 people under 65 went without a prescription drug because they couldn’t afford it, according to the Center for Studying Health System Change in Washington, D.C.

The current figure may be even higher because of the recent economic downturn, said Laurie E. Felland, a senior health researcher at the center and lead author of the study.

“Our findings are particularly troublesome given the increased reliance on prescription drugs to treat chronic conditions,” she added. “People who go without their prescriptions experience worsening health and complications.”