Medicare does not cover most prescription medicines given outside a hospital. It is this gap in coverage that Congress is working to fill.
The study, being released Thursday, is more evidence of the racial gulf in health and health coverage, and points out that the prescription drug legislation could help remedy the problem.
"There's no question that the lack of Medicare prescription drug coverage falls disproportionately on African-American seniors," said Paul Ginsburg, president of the Center for Studying Health System Change, which conducted the study.
The study is based on a 2001 survey of 60,000 people, including about 7,770 elderly Medicare recipients.
It found that 16.4 percent of elderly blacks reported they could not afford to fill at least one prescription in the previous year. The rate among whites was 6.8 percent.
Researchers found that nearly half of the gap is attributable to differences in income, supplemental insurance and chronic conditions. As a group, whites are wealthier, more likely to have private insurance and less likely to have chronic conditions.
A small portion of the gap can be explained by factors such as gender, age, family size and education.
The rest, researchers say, may be due to differences in the amount of savings people have and other factors.
Whites on average are expected to live almost six years longer than blacks, according to statistics from the Centers for Disease Control and Prevention. A white person born in 2000 was expected to live 77.4 years, while a black counterpart could expect to live 71.7 years.
Congress is now trying to reconcile competing House and Senate versions of a plan to add prescription drug coverage to Medicare. That will require ending disagreements about private sector involvement, means testing and tax-sheltered medical savings accounts.