Studies of any design that reported on use of two non-clozapine antipsychotic drugs in adults with schizophrenia were eligible for the review. Studies reporting outcomes related to clinical effectiveness or safety were included.
The review assessed quetiapine augmentation, and seven different combinations and doses of two of the following drugs: amisulpride, aripiprazole, olanzapine, quetiapine, risperidone and ziprasidone. Most of the included studies did not use rating scales to assess outcomes.
Most participants had a diagnosis of schizophrenia, but some had schizo-affective disorder. Indications for combination treatment were treatment-resistant schizophrenia or reduction of adverse effects. Duration of monitoring, where reported, ranged from a few days to over a year.
The authors did not state how studies were selected for the review.