A Massachusetts law passed in 2006 that expanded insurance coverage did not lead to an increase in the number of state residents who received inpatient treatment for drug and alcohol abuse at state-contracted facilities, according to a new study.

The study’s authors say their findings indicate that increasing coverage is not enough to boost treatment use. “Changes in eligibility, services, financing, system design, and policy may also be required,” they note in the journal Health Affairs.

The number of admissions for substance use disorders at treatment centers in Massachusetts held steady at slightly more than 100,000 per year between 2006 and 2010, The Boston Globe reports.

Lead author Victor Capoccia of the University of Wisconsin-Madison told the newspaper that Massachusetts has a better system of care than many states. He noted his findings should serve as a warning to other states that simply expanding insurance under the Affordable Care Act starting in 2014 will not be enough to provide patients the care they need.

Michael Botticelli, Director of the Massachusetts Bureau of Substance Abuse Services, said it can be difficult to get people with substance use disorders, particularly young adults, to enroll in health insurance plans, even if they qualify for assistance. “Self-care behavior is not the hallmark of people with addictive disorders,” he said. Botticelli added the state is trying to get more addiction services into primary care settings.