Changes in Access to Substance Use Disorder Treatment Associated with the 2008 U.S. Parity Law

Historically, U.S. health insurance plans included fewer and more restrictive benefits for mental health (MH) and substance use disorder (SUD) treatment compared to general medical care. The 2008 Mental Health Parity and Addiction Equity Act (MHPAEA) mandated that group-based private health plans covering MH/SUD treatment do so in a way no more restrictive than coverage for general medical care. Multiple rounds of rulemaking, including 2024 final rules most recently, have strengthened federal regulation of plans' non-quantitative treatment limits (NQTLs).

To investigate how SUD treatment rates, perceived unmet needs, and barriers to treatment changed for adults with group-based private insurance following MHPAEA.

We conducted a secondary analysis of annual, cross-sectional data from the National Survey on Drug Use and Health (2006-2014) with a sample of adults aged 18-64 years meeting criteria for SUD treatment need. We used difference-in-differences models to estimate and compare outcomes between adults with group-based private insurance (GBPI) and multiple comparison groups including those with individual-based private insurance (IBPI) before (2006-2009) and after (2011-2014) MHPAEA implementation.

Among 32,605 survey respondents with SUD (weighted N=16,108,465), 17,065 individuals had GBPI. For this group, adjusted rates of any past-year SUD treatment remained low, and we did not detect a statistically significant change following MHPAEA implementation (6.4% pre-parity vs. 7.0% post-parity; +0.5 percentage points, 95% CI: -1.1 to 2.2, p=0.514). Difference-in-differences analysis showed no significant difference in changes between those with GBPI and those with IBPI (+3.1 percentage points, 95% CI: -3.8 to 10.0, p=0.380). Self-identified unmet SUD treatment need also remained consistently low (3.9% pre-parity vs. 3.9% post-parity; +0.1 percentage points, 95% CI: -1.0 to 1.1, p=0.895). Among GBPI enrollees reporting unmet need, no significant changes were observed in barriers related to cost (14.9% post-MHPAEA), treatment accessibility (22.8%), ambivalence about seeking treatment (66.8%), or stigma (19.1%). Only half of GBPI enrollees knew their insurance covered SUD treatment, with nearly 40% reporting they didn't know.

These findings align with other studies of U.S. parity laws, which have found little to no impact on SUD treatment rates despite potential improvements in financial protection. Limitations include reliance on self-reported data, inability to identify specific insurance plans exempt from MHPAEA, and lack of state-level identifiers to account for pre-existing state parity laws.

Providers and health systems may consider new strategies to identify SUD treatment needs and improve awareness of insurance coverage among patients, as nearly four in 10 individuals with group-based private insurance and SUD were unaware of their SUD coverage.

While recent MHPAEA final rules strengthened enforcement mechanisms and prohibit restrictive NQTLs, our findings suggest additional policies may be needed to improve access to SUD treatment, including efforts to increase awareness of treatment need and coverage, reduce stigma, and enhance treatment availability.

Future research could examine how the 2024 MHPAEA final rules affect NQTLs and investigate the combined effects of MHPAEA with other health reforms on SUD treatment access and strategies to overcome persistent non-financial barriers to treatment.