A new study examined the effects of the 2006 healthcare expansion in Massachusetts, and found a drop in the rate of hospital-based mental health care for those under 26.

Critics of healthcare expansion in the U.S. argue that it will increase the number who people who seek treatment in costly emergency rooms.

A Science study published in January found that poor people in the Portland area given Medicaid coverage went to the emergency room 40 percent more than those without health insurance.

Unlike a broken leg, a mental health condition doesn’t have to be treated by an ER doctor. Still, many undiagnosed young adults come in contact with mental health services on an emergency basis.

Community hospitals account for 60 percent of inpatient mental health spending and 70 percent of spending for substance abuse disorders. So researchers at the Dartmouth Institute for Health Policy and Clinical Practice and other institutions wanted to know what effect, if any, expanded public healthcare coverage would have on the use of these services.

After examining Massachusetts’ 2006 healthcare expansion—which contained many provisions similar to the Affordable Care Act—they discovered that fewer people ages 19 to 25 sought care for mental health and substance abuse in ERs compared to states without the extended coverage.

“Expanded health insurance coverage for young adults is not associated with large increases in hospital-based care for behavioral health, but it increased financial protection to young adults with behavioral health diagnoses and to the hospitals that care for them,” the authors concluded in their study published Wednesday in the American Medical Association’s journal Psychiatry.

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The Massachusetts healthcare expansion allowed young adults to stay on their parents’ insurance plans until the age of 26, and also mandated that coverage for mental health and substance abuse match coverage for medical and surgical services. These two provisions are also included in the Affordable Care Act, better known as Obamacare.

Because 75 percent of mental health disorders manifest by the age of 25, researchers focused on the 19 to 25 demographic, who also tend to be uninsured. The Massachusetts reform lowered the rate of uninsured patients in the state from 26 percent to 10 percent.

Using outpatient community hospital data for 48,889 mental health diagnoses from 2003 to 2009, researchers found that the statewide change in insurance benefits resulted in a significant decrease in hospital and emergency room admissions for mental health and substance abuse issues.

To researchers, this showed that outpatient treatment and primary care use increased with expanded insurance coverage, which lowered out-of-pocket costs for young adults seeking treatment.

Researchers did note that emergency room visits for mental health problems overall increased after 2006, but the increase was far less than in nearby Maryland.

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The study authors acknowledge a few shortcomings of their research, especially that it didn’t examine individual outcomes for patients, so the study authors don’t know whether the care patients received was effective.

Also, Massachusetts’ healthcare system has more than twice the average number of psychiatrists per resident than the U.S. as a whole.

And expanded health insurance coverage isn’t a magic bullet for increasing mental health coverage. A separate study published in JAMA Psychiatry found that only about 55 percent of psychiatrists in private practice accept private insurance plans or Medicaid, while nearly 90 percent of doctors in other fields do.

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