Mental Health Parity and Addiction Equity Act and the Use of Outpatient Behavioral Health Services in the United States, 2005-2016.

Objectives. To assess the impact of the 2008 Paul Wellstone and Pete Domenici Mental Health Parity and Addiction Equity Act (MHPAEA) on mental and substance use disorder services in the private, large group employer-sponsored insurance market in the United States. Methods. We analyzed data from the IBM MarketScan Commercial Database from January 2005 through September 2015 by using population-level interrupted time series regressions to determine whether parity implementation was associated with utilization and spending outcomes. Results. MHPAEA had significant positive associations with utilization of mental and substance use disorder outpatient services. A spending decomposition analysis indicated that increases in utilization were the primary drivers of increases in spending associated with MHPAEA. Analyses of opioid use disorder and nonopioid substance use disorder services found that associations with utilization and spending were not attributable only to increases in treatment of opioid use disorder. Conclusions. MHPAEA is positively associated with utilization of outpatient mental and substance use disorder services for Americans covered by large group employer-sponsored insurance. Public Health Implications. These trends continued over the 5-year post-MHPAEA period, underscoring the long-term relationship between this policy change and utilization of behavioral health services.