FRIDAY, Aug. 26, 2016 (HealthDay News) -- Though a growing number of Americans are able to afford prescription medications, millions still have difficulty, a new study finds.

At the recession's height in 2009, over 25 million Americans said they had not filled a prescription in the previous year because they couldn't afford it, the analysis of federal government data showed. That was nearly one in 10 Americans.

Between 1999 and 2009, every age group except seniors found prescription drugs increasingly difficult to afford. Among seniors, the problem was worst in 2004, when 5.4 percent were unable to afford their medicine. In 2006, once the new Medicare Part D program was in place, that number fell to 3.6 percent, the study found.

The Affordable Care Act, also called Obamacare, was signed into law by President Barack Obama in 2010.

Most groups now have greater ability to afford prescription drugs, the researchers said. For example, the percentage of 19- to 25-year-olds who couldn't afford to fill a prescription fell from nearly 11 percent in 2010 to just over 8 percent in 2011, as the Affordable Care Act let young adults remain on their parents' health insurance.

Among 26- to 64-year-olds, the percentage who struggled to afford prescriptions fell from 9 percent in 2013 to just under 8 percent in 2014, the researchers from Washington State University (WSU) found.

"The takeaway is that health policy matters," study leader Jae Kennedy said in a university news release. Kennedy is chair of the department of health policy and administration in WSU's College of Nursing.

The researchers estimated that 16.4 million Americans still find it hard to afford prescriptions. That number could be reduced if more states opted to participate in Medicaid expansion, the study authors suggested.

Medicaid expansion is a provision of the Affordable Care Act that extends health coverage to more low-income families through the Medicaid program.

The findings were published Aug. 23 in the American Journal of Public Health.

More information

The U.S. National Library of Medicine outlines how to save money on medicines.