Substance use and co-occurring mental health disorders in the Deep South United States: a comprehensive analysis of mental health client-level data

Background: Substance use and co-occurring mental health disorders remain critical public health challenges in the Deep South, with substantial variation observed across states.Objective: This study examined the associations between substance use and co-occurring mental health disorders and explored state-level variations.Methods: We conducted a cross-sectional analysis of 428,809 participants in the Deep South using the 2023 SAMHSA MH-CLD dataset. Multivariable regressions were used to assess the associations, with subgroup analyses examining state-level variation. Additionally, hierarchical regressions were used to provide a robust and sensitive evaluation of the primary finding.Results: The cohort was predominantly female (52.96%), White (51.36%), and aged 40–59 years (27.43%). Associations between substance use and mental health disorders varied significantly across Deep South states. In Louisiana, depression was most strongly associated with alcohol (aOR: 1.85, 95% CI: 1.51–1.72) and cannabis use (aOR: 1.38, 95% CI:1.24–1.52), while in Alabama, opioid use showed the highest association with depression (aOR: 1.74, 95% CI: 1.51–1.84). In Mississippi, cocaine use showed the strongest association with depression (aOR: 1.74, 95% CI: 1.35–2.01). Bipolar disorder demonstrated the strongest links with substance use in Alabama, whereas personality disorder was most associated with cocaine in Louisiana (aOR: 3.72, 95% CI: 3.25–4.21), and opioid in South Carolina (aOR: 2.49, 95% CI: 2.25–2.65).Conclusion: Substance use and co-occurring mental health disorders varied significantly across Deep South states, highlighting the need for state-specific behavioral health strategies. Observed state-level variations may reflect differences in population characteristics, healthcare access, and behavioral health systems across the region.