ALEM, Ore. (AP) — A new study has found that previously uninsured people who were given health coverage through Medicaid used the emergency room 40 percent more than others who weren't able to join the program.

The findings were published Thursday by the journal Science. They suggest that hospitals and health officials around the nation need to be prepared for an increase in emergency room trips as millions of Americans gain insurance this week under the federal health care law, many of them through Medicaid.

Researchers looked at 25,000 people in the Portland, Ore., metro area in a randomized, controlled experiment that allowed researchers to pinpoint Medicaid coverage as the cause of the higher use.

The study was done by researchers at Harvard, the Massachusetts Institute of Technology and the National Bureau of Economic Research.