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

Background: Cannabis use is common among individuals with substance use disorders (SUDs), yet its relationship with mental health characteristics in treatment-seeking populations remains unclear. Objectives: 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. Methods: 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; n = 363), lifetime use but no past-year use (past use; n = 109), and no lifetime use (never use; n = 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. Results: 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 (p < 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 (p < 0.001); the past use group had the highest scores (p < 0.05), and these associations persisted when controlling for trauma history. Conclusions: Lifetime cannabis use was associated with poorer mental health characteristics among patients seeking treatment for SUDs, possibly due to greater incidence of trauma.