DSM-V research agenda: substance abuse/psychosis comorbidity.

For diagnosis of patients with comorbid psychotic symptoms and substance use disorders (SUDs), Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, makes clear distinctions between independent psychotic disorders (eg, bipolar disorder, schizophrenia) and substance-induced syndromes (eg, delirium, dementias). Most substance-induced psychotic symptoms are considered to be short lived and to resolve with sustained abstinence along with other symptoms of substance intoxication and withdrawal. These guidelines are challenged by practical difficulties in distinguishing between substance-induced and independent psychoses and by mounting evidence that marijuana use may be a contributing cause of schizophrenia. To inform the diagnostic distinction between substance-induced vs independent psychotic symptoms, 2 kinds of information could be sought from longitudinal research: (a) identification of early markers that clearly differentiate the 2 conditions and (b) more precise information about duration of psychotic symptoms induced by different substances. Evidence of this type could emerge from reanalysis of existing data from large-scale longitudinal studies of community samples. To inform possible nosological changes related to the possible schizophrenia-inducing role of marijuana (eg, designating a "cannabis-induced" subtype), a wide range of research evidence will be needed to clarify the relationship between effects of cannabis and schizophrenia symptoms. Ultimately, the ideal psychiatric nomenclature will define syndromes on the basis of established etiology and/or pathophysiology. Given the strong association between SUDs and psychotic disorders, research on the neurobiology of psychotic disorders could fruitfully include subjects with comorbid SUDs to shed light on shared etiology and pathophysiology.