Neurobiology of Comorbid Substance Use Disorders and Psychiatric Disorders Current State of Evidence

Background: "Dual disorder'' or "dual diagnosis'' refers to the co-occurrence of substance use disorder and psychiatric disorders. Prospective studies have shown that treatment outcomes, such as symptom levels, hospitalization rates, housing stability, and functional status, are worse among the patients with dual disorders as compared with those who have either of these disorders. Objectives: The current article is aimed at reviewing the current state of evidence on neurobiology of dual disorders. Given the high prevalence of co-occurrence of substance use disorder and psychiatric disorders, it is important to explore the various facets of this association. The current review assimilates the information on neurobiological research on dual disorders and helps the readers gain insights into the current understanding on this theme. Methods: The electronic database of PubMed was searched for relevant publications. Results: The studies included in the review belonged to various domains of neurobiology including neuropathology, structural neuroimaging, functional neuroimaging, genetics, neurochemicals/neuroreceptors, and neuroendocrinology. Forty studies were included in the review. Conclusions: Most of the issues related to the neurobiology of dual disorders remain inadequately studied. However, the current evidence suggests that the individuals with co-occurring disorders are likely to differ from those with either substance use disorders or psychiatric disorders alone on various neurobiological aspects. Hence, it is imperative to systematically study the various neurobiological aspects of dual disorders in the future.