Impact of Co-Occurring Psychiatric Comorbidities and Substance Use Disorders on Outcomes in Adolescents and Young Adults with Opioid Use Disorder: A Retrospective Cohort Study

<b>Background/Objectives:</b> Adolescents and young adults (AYAs) with opioid use disorder (OUD) frequently have co-occurring psychiatric conditions and substance use disorders (SUDs). This study evaluated the association of psychiatric comorbidities and other SUDs with treatment retention and urine drug test (UDT) results in AYAs with OUD. <b>Methods:</b> This retrospective cohort study included AYAs enrolled in the Substance Use Treatment and Recovery clinic from 2009 to 2022. Participants were categorized into four groups: no comorbidities, only mental health disorders, only other SUDs, and both disorders. Treatment outcomes included retention time and UDT results for medication for OUD (MOUD) and illicit substances, including tetrahydrocannabinol (THC). Kruskal-Wallis tests were used to evaluate differences across groups, and regression models identified variables associated with outcomes. Statistical significance was set at <i>p</i> < 0.05. <b>Results:</b> Among 157 patients, the median retention time was 300 days. Depression (<i>p</i> = 0.04), post-traumatic stress disorder (<i>p</i> = 0.002), and alcohol use disorder (<i>p</i> = 0.04) were associated with prolonged retention, whereas cannabis use disorder predicted shorter retention (<i>p</i> = 0.02). The median proportion of positive UDTs was 0.9 for MOUD, 0.1 for illicit substances, and 0.0 for THC. Older age (<i>p</i> = 0.02) and the use of antidepressants and anxiolytics were associated with greater adherence to MOUD. Cannabis use disorder (<i>p</i> = 0.02) and male sex (<i>p</i> = 0.04) predicted positive UDTs for THC, while MOUD use was linked to lower THC positivity (<i>p</i> = 0.02). The main limitations of this study were related to its retrospective study design and single-center setting. <b>Conclusions:</b> Psychiatric and substance use comorbidities significantly influence retention and treatment adherence in AYAs with OUD. Integrated treatment may improve engagement and outcomes. Further research is needed to tailor interventions for AYAs with co-occurring disorders.