Via NY Times:

Supporters of President Obama’s health care law had predicted that expanding insurance coverage for the poor would reduce costly emergency room visits as people sought care from primary care doctors. But a rigorous new study conducted in Oregon has flipped that assumption on its head, finding that the newly insured actually went to the emergency room more often.

The study, published in the journal Science, compared thousands of low-income people in the Portland area who were randomly selected in a 2008 lottery to get Medicaid coverage with people who entered the lottery but remained uninsured. Those who gained coverage made 40 percent more visits to the emergency room than their uninsured counterparts. The pattern was so strong that it held true across most demographic groups, times of day, and types of visits, including for conditions that were treatable in primary care settings.

The finding casts doubt on the hope that expanded insurance coverage will help rein in rising emergency room costs just as more than two million people are gaining coverage under the Affordable Care Act.

Instead, the study suggests that the surge in the numbers of insured people may put even greater pressure on emergency rooms and increase costs. Nearly 30 million uninsured Americans could gain coverage under the law, about half of them through Medicaid. The first policies took effect on Wednesday.

“I suspect that the finding will be surprising to many in the policy debate,” said Katherine Baicker, an economist at Harvard University’s School of Public Health and one of the authors of the study.