Associations Between Cannabis Use and Mental Health in Patients Accessing Treatment for Substance Use Disorders: An Exploratory Cross-Sectional Study

<i>Background</i>: Cannabis use is common among individuals with substance use disorders (SUDs), yet its relationship with mental health characteristics in treatment-seeking populations remains unclear. <i>Objectives</i>: This study examined associations between cannabis use and mental health in patients seeking SUD treatment, to understand whether cannabis use relates to clinical characteristics relevant to SUD care. <i>Methods</i>: A cross-sectional online survey was completed by 544 patients in Ontario, Canada seeking treatment for any SUD (including cannabis use disorder). Participants were grouped by cannabis use: any past-year use (current use; <i>n</i> = 363), lifetime use but no past-year use (past use; <i>n</i> = 109), and no lifetime use (never use; <i>n</i> = 72). Anxiety, depression, sleep quality, and disability were assessed with the Generalized Anxiety Disorder scale (GAD-7), Patient Health Questionnaire (PHQ-9), Pittsburgh Sleep Quality Index (PSQI), and World Health Organization Disability Assessment Schedule (WHODAS). Psychiatric diagnoses, trauma exposures, and suicidality were also assessed. <i>Results</i>: Cannabis use group was significantly associated with trauma history and several psychiatric diagnoses (e.g., anxiety, depression), with the highest prevalence in the current use group (<i>p</i> &lt; 0.05). Many associations between cannabis use and psychiatric diagnoses were no longer significant after controlling for trauma history. GAD-7, PHQ-9, WHODAS, and PSQI scores significantly differed between groups (<i>p</i> &lt; 0.001); the past use group had the highest scores (<i>p</i> &lt; 0.05), and these associations persisted when controlling for trauma history. <i>Conclusions</i>: Lifetime cannabis use was associated with poorer mental health characteristics among patients seeking treatment for SUDs, possibly due to greater incidence of trauma.