Risk of readmission among individuals with cannabis use disorder during a 15-year cohort study: the impact of socio-economic factors and psychiatric comorbidity.

ABSTRACT

BACKGROUND AND AIM: Cannabis use disorder (CUD) is one of the main reasons for seeking substance treatment in the Nordic countries, but there are few studies on readmission to care. We aimed to characterize CUD readmission and estimate the magnitude of how socio-economic factors and psychiatric comorbidity influence the risk of CUD readmission. DESIGN, SETTING AND PARTICIPANTS: This was a nation-wide cohort study carried out between 2001 and 2016 in Sweden. The participants were individuals with CUD, aged 17 years and above (n = 12 143). MEASUREMENTS Information on predictors was obtained from registers and included education, income and psychiatric comorbidity assessed by six disease groups. The outcome measure was readmission, defined as a CUD visit to health-care at least 6 months after initial CUD diagnosis. Hazard ratios (HR) were estimated using Cox survival analyses and flexible parametric survival analyses to assess risk of readmission and how the risk varied with age. FINDINGS: The vast majority of CUD visits took place in outpatient care (~80%). Approximately 23% of the included individuals were readmitted to care during follow-up. The fully adjusted model showed an increased risk of readmission among those with schizophrenia and other psychotic disorders [HR = 1.54, 95% confidence interval (CI) = 1.29-1.84], low education (HR = 1.40, 95% CI = 1.24-1.57), personality disorders (HR = 1.27, 95% CI = 1.05-1.54) or mood disorders (HR = 1.27, 95% CI = 1.12-1.45). Flexible parametric modeling revealed increased risk of readmission mainly in individuals aged 18-35 years. CONCLUSIONS: The risk of readmission was highest among those with low education, schizophrenia and other psychotic disorders, mood-related disorders or personality disorders. Individuals aged 18-35 years showed the highest risk of readmission. Our findings highlight individuals with complex health-care needs.