Aims: Addiction is a frequent comorbid disorder in schizophrenia and associated with poor outcome. The present study sought to determine whether addicted and non-addicted schizophrenic patients are impaired differentially on the executive abilities of working memory and multi-tasking which are relevant for maintaining abstinence.

Design: Comparisons of executive performance in clinical and control groups.

Setting: In-patient setting.

Participants: The cognitive profile of schizophrenic patients with and without comorbid substance abuse disorder was compared with that of patients suffering from major depression or alcoholism and healthy participants.

Measurements: A range of cognitive tasks was used to assess: (i) the ability to update continuously context information in working memory and to use it for action selection; and (ii) the capacity to divide attention between different sensory input channels and to coordinate verbal and manual responses.

Findings: Single-diagnosis schizophrenic patients showed pronounced impairments on measures of online maintenance and use of context information. Their ability to coordinate different sensory input channels (divided attention) was also impaired. Addicted schizophrenics showed evidence of impaired sensory input management and of reduced context sensitivity, when age differences were controlled.

Conclusions: The present study indicates severe working memory and multi-tasking deficits in schizophrenia which are, however, not exacerbated by comorbid addiction.