Treatment retention and abstinence of patients with substance use disorders according to addiction severity and psychiatry comorbidity: A six-month follow-up study in an outpatient unit

Introduction: The impact of psychiatric comorbidity and addiction features throughout the course of addiction has been widely studied. This is a naturalistic study conducted in an outpatient unit, where treatment follow-up studies are scarce compared to studies including inpatients or those under experimental conditions. Therefore, this follow-up study aims to analyze the treatment adherence and abstinence of outpatients with SUD (Substance Use Disorders) according to addiction severity and psychiatric comorbidity. Methods: The current six-month follow-up study examined 404 SUD outpatients. Psychiatric comorbidity, addiction severity, substance consumption and treatment adherence were systematically evaluated using semi-structured interviews. Survival analyses were conducted to compare the time of treatment adherence and abstinence in a bivariate and multivariate level. Results: A progressive dropout was observed, reaching 32.2% of dropouts at the six-month follow-up. More than 50% achieved abstinence during the first month and similar percentages were found until the six-month follow-up. At the multivariate level, treatment adherence, cannabis use disorder and polyconsumption were independently associated with earlier dropout. ADHD was the only mental disorder significantly related with dropout. Regarding substance consumption, the time of abstinence was independently associated with months of treat-ment adherence and the achievement of abstinence before starting treatment. In general, dual diagnosis was associated with less time of abstinence, but only depressive disorder across the lifespan was related to less time of abstinence in the multivariate model. Conclusion: These findings highlight the importance of an accurate diagnosis at the beginning of treatment, especially in an outpatient setting, addressing the treatment needs and promoting strategies that improve treatment adherence and reduce the risk of relapses.