The percentage of low-income Americans with substance use disorders who were uninsured declined more sharply in states that chose to expand Medicaid under the Affordable Care Act versus states that did not, according to a new study. The percentage of low-income residents with substance use disorders without coverage decreased from 34 percent in 2013 to 20 percent in 2015 within states that had implemented Medicaid expansion — or expansion states — compared to 45 percent to 39 percent in non-expansion states.