Literature Collection

"Dual disorders" (DD) refers to the co-occurrence of addiction and other mental health conditions, which often interact and complicate care. Despite scientific evidence showing shared brain mechanisms, current diagnostic systems treat them separately, leading to fragmented treatment and stigma. The World Association on Dual Disorders urges adopting "dual disorders" as a unified term to improve clarity, care integration, and outcomes.

The coexistence of substance use disorders (SUD) and other mental disorders - commonly referred to as dual disorders (DD) - is highly prevalent and clinically significant. Although various terms have been used over time (e.g., psychiatric comorbidity, dual pathology), the lack of a standardised definition has created inconsistencies in diagnosis, communication, research, and treatment. Epidemiological studies estimate that 30-80% of individuals with SUD have co-occurring psychiatric disorders, with prevalence depending on the substance involved, gender, age, and the population studied (general population, people in emergency rooms, mental health addiction facilities, harm reduction facilities, prison). Compared to individuals with a single disorder, people with DD exhibit more severe psychopathological symptoms, higher suicide risk, increased relapse rates, poorer treatment adherence, more medical comorbidities, and worse psychosocial outcomes, including unemployment, homelessness, and social exclusion. Despite extensive evidence, both SUD and other mental disorders often remain underdiagnosed and undertreated, partly due to diagnostic complexities such as overlapping symptomatology and the syndromic nature of psychiatric classifications. Additional barriers include the structural separation between mental health and addiction services and limited integrated care expertise. The "wrong door syndrome" exemplifies how patients are frequently directed to services unable to address both conditions, leading to suboptimal outcomes. Furthermore, individuals with DD are often excluded from clinical research, limiting the evidence base for tailored interventions. Improving the detection and treatment of DD is a major challenge for mental health and addiction systems. Integrated, holistic treatment approaches from the outset are essential to optimise outcomes for this highly vulnerable population.

BACKGROUND: Mental health diagnoses (MHD) are common among those with opioid use disorders (OUD). Methadone/buprenorphine are effective medication-assisted treatment (MAT) strategies; however, treatment receipt is low among those with dual MHDs. Medicaid expansions have broadly increased access to OUD and mental health services over time, but MAT uptake may vary depending on multiple factors, including MHD status, state Medicaid expansion decisions, and race/ethnicity and gender. Examining clinical and policy approaches to promoting MAT uptake may improve services among marginalized groups. METHODS: MAT treatment discharges were identified using the Treatment Episodes Dataset-Discharges (TEDS-D; 2014-2017) (n = 1,400,808). We used multivariate logistic regression to model MAT receipt using interactions and adjusted for several potential confounders. RESULTS: Nearly one-third of OUD treatment discharges received MAT. Dual MHDs in both expansion and non-expansion states were positively associated with MAT uptake over time. Dual MHDs were negatively associated with MAT receipt only among American Indian/Alaska Native women residing in Medicaid expansion states (aOR = 0.58, 95 % CI = 0.52-0.66, p < 0.0001). CONCLUSION: Disparities in MAT utilization are nuanced and vary widely depending on dual MHD status, Medicaid expansion, and race/ethnicity/gender. Medicaid is beneficial but not a universal treatment panacea. Clinical decisions to initiate MAT are dependent on multiple factors and should be tailored to meet the needs of high-risk, historically disadvantaged clients.