Specialty Substance Use and Mental Health Treatment Use among U.S. Adults with Substance Use Disorder: Associations with Substance Use Disorder and Mental Illness Severity

U.S. adults with substance use disorders (SUD) underutilize specialty substance use treatment (SUT) and are more likely to use mental health treatment (MHT) than SUT. In this study based on the 2022 and 2023 National Survey on Drug Use and Health (N=19,555, age 18+ with past-year SUD), we examined clinical and other factors associated with four distinct behavioral health service configurations: no treatment, both SUT and MHT, SUT only, and MHT only. We fitted two multinomial and binary logistic regression models to examine associations of treatment use patterns with SUD and mental illness severity as need factors, while controlling for predisposing, enabling, and other need factors. The findings show that 59.3% U.S. adults with SUD did not use SUT or MHT in the past year, 10.7% used both SUT and MHT, 3.7% used SUT only, and 26.4% used MHT only. Severe SUD (RRR=2.77, 95% CI=2.13-3.60), compared with mild SUD, and all levels of mental illness severity (RRR=7.27, 95% CI=5.41-9.79 for serious mental illness) were associated with a higher likelihood of receiving both SUT and MHT. Both moderate and severe SUD, but not mental illness severity, were associated with receiving SUT only. All levels of mental illness severity were also associated with a higher likelihood of receiving MHT only (RRR=7.30, 95% CI=6.17-8.64 for serious mental illness), whereas severe SUD was associated with a lower likelihood of receiving MHT only. The findings were similar in analyses restricted to users of any treatment or SUT. In sum, receipt of both SUT and MHT is concentrated among individuals with the highest clinical severity in both SUD and mental illness. These findings underscore the importance of integrating substance use and mental health services.