Neuropsychology of dual diagnosis: Understanding the combined effects of schizophrenia and substance use disorders

Empirical studies of cognitive functioning in patients suffering from schizophrenia and a substance use disorder are lacking. Consensus exists that schizophrenia is a neurobehavioral disorder with cognitive deficits. With this ready explanation for cognitive impairment in schizophrenia, there exists the possibility that other treatable sources of cognitive decline in schizophrenia, such as substance abuse, may be ignored. The cognitive impairments (e.g., abstraction, selective attention, effortful processing, episodic memory and denial of deficits/illness) and biologic abnormalities (e.g., reduced P300 amplitude, enlarged ventricles, and hypofrontality) common to both schizophrenia and substance use disorders are reviewed. Differences in the cognitive status of the disorders are also noted. Factors altering the cognitive status of these patients are discussed, and seven potential frameworks are offered for conceptualizing the etiologic relation and cognitive impact of these disorders.