Co-Occurrence of Substance use Disorders with other Psychiatric Disorders: Implications for Treatment Services

Introduction This paper critically evaluates the literature on the co-occurrence of substance-use disorders (SUDs) with other psychiatric conditions. Our review considers the variety of different associations between the two, and suggests the implications of the literature for the design of treatment services that address both types of disorders. Methods: A narrative review of research and theory was conducted, covering epidemiology of co-occurring psychiatric disorders worldwide, mechanisms underlying co-occurrence, and treatment models. Results: Epidemiological research has documented a high prevalence of co-occurring disorders in both clinical samples and the general population, although the literature is based primarily on studies in high-income countries and some of the overlap might be due to the co-occurrence of milder forms of both types of disorders. Consistent with what has been reported in other reviews, we conclude that clients with co-occurring disorders tend to have a more severe course of illness, more severe health and social consequences, more difficulties in treatment, and worse treatment outcomes than clients with a single disorder; we address the implications of these findings for the design of treatment services. Conclusions: Much of the evidence shows that separately, treatments for both SUD and other psychiatric disorders are effective in reducing substance use and in improving behavioral, familial, and psychosocial outcomes. The evidence further suggests that these outcomes might be improved when treatment modalities are offered in combination within an integrated treatment plan that simultaneously addresses substance abuse and psychiatric problems. It is concluded that there is potentially more to be gained from taking a public health perspective and working on efforts to implement existing evidence-based practices at the systems level, than from the current tendency to look for ever more powerful individual-level interventions at the clinical level.