A new study by researchers at the Massachusetts Institute of Technology and the Harvard School of Public Health has found that adults who have health insurance through the Medicaid program use emergency rooms 40 percent more than those who do not have health insurance.

The study looked at adults in Oregon who were able to get access to Medicaid coverage through a lottery. The researchers reviewed emergency room records for about 25,000 people over 18 months.

“When you cover the uninsured, emergency room use goes up by a large magnitude [and] these results suggest that other Medicaid expansions are unlikely to decrease emergency room use. “says Amy Finkelstein, a professor of economics at MIT and a principal investigator of the study.

Through their records review the researchers found that having Medicaid increased visits to the emergency room across several demographic groups and types of medical visits and medical conditions, including conditions that could have been treated by community health providers.

The researchers say their findings are very relevant right now because many states have expanded Medicaid coverage for adults, with that coverage beginning this month, under the Affordable Care Act. However, one goal of the Medicaid expansion is to decrease use of emergency rooms for routine care in order to save health care costs. Some news reports about the study, including the New York Times, suggested that the new Medicaid beneficiaries may have sought care at emergency rooms because they didn’t know how to access primary care providers in the community. Many state and local health departments including the San Francisco health department, list community clinics, along with services and hours, on their website to help  people find community health resources.

The study was published in Science.