Increasing numbers of reports concerning diabetes, ketoacidosis, hyperglycaemia and lipid dysregulation in patients treated with second-generation (or atypical) antipsychotics have raised concerns about a possible association between these metabolic effects and treatment with these medications. This comprehensive literature review considers the evidence for and against an association between glucose or lipid dysregulation and eight separate second-generation antipsychotics currently available in the US and/or Europe, specifically clozapine, olanzapine, risperidone, quetiapine, zotepine, amisulpride, ziprasidone and aripiprazole. This review also includes an assessment of the potential contributory role of treatment-induced weight gain in conferring risk for hyperglycaemia and dyslipidaemia during treatment with different antipsychotic medications. Substantial evidence from a variety of human populations, including some recent confirmatory evidence in treated psychiatric patients, indicates that increased adiposity is associated with a variety of adverse physiological effects, including decreases in insulin sensitivity and changes in plasma glucose and lipid levels. Comparison of mean weight changes and relative percentages of patients experiencing specific levels of weight increase from controlled, randomised clinical trials indicates that weight gain liability varies significantly across the different second generation antipsychotic agents. Clozapine and olanzapine treatment are associated with the greatest risk of clinically significant weight gain, with other agents producing relatively lower levels of risk. Risperidone, quetiapine, amisulpride and zotepine generally show low to moderate levels of mean weight gain and a modest risk of clinically significant increases in weight. Ziprasidone and aripiprazole treatment are generally associated with minimal mean weight gain and the lowest risk of more significant increases. Published studies including uncontrolled observations, large retrospective database analyses and controlled experimental studies, including randomised clinical trials, indicate that the different second-generation antipsychotics are associated with differing effects on glucose and lipid metabolism. These studies offer generally consistent evidence that clozapine and olanzapine treatment are associated with an increased risk of diabetes mellitus and dyslipidaemia. Inconsistent results, and a generally smaller effect in studies where an effect is reported, suggest limited if any increased risk for treatment-induced diabetes mellitus and dyslipidaemia during risperidone treatment, despite a comparable volume of published data. A similarly smaller and inconsistent signal suggests limited if any increased risk of diabetes or dyslipidaemia during quetiapine treatment, but this is based on less published data than is available for risperidone. The absence of retrospective database studies, and little or no relevant published data from clinical trials, makes it difficult to draw conclusions concerning risk for zotepine or amisulpride, although amisulpride appears to have less risk of treatment-emergent dyslipidaemia in comparison to olanzapine. With increasing data from clinical trials but little or no currently published data from large retrospective database analyses, there is no evidence at this time to suggest that ziprasidone and aripiprazole treatment are associated with an increase in risk for diabetes, dyslipidaemia or other adverse effects on glucose or lipid metabolism. In general, the rank order of risk observed for the second-generation antipsychotic medications suggests that the differing weight gain liability of atypical agents contributes to the differing relative risk of insulin resistance, dyslipidaemia and hyperglycaemia. This would be consistent with effects observed in nonpsychiatric samples, where risk for adverse metabolic changes tends to increase with increasing adiposity. From this perspective, a possible increase in risk would be predicted to occur in association with any treatment that produces increases in weight and adiposity. However, case reports tentatively suggest that substantial weight gain or obesity may not be a factor in up to one-quarter of cases of new-onset diabetes that occur during treatment. Pending further testing from preclinical and clinical studies, limited controlled studies support the hypothesis that clozapine and olanzapine may have a direct effect on glucose regulation independent of adiposity. The results of studies in this area are relevant to primary and secondary prevention efforts that aim to address the multiple factors that contribute to increased prevalence of type 2 diabetes mellitus and cardiovascular disease in populations that are often treated with second-generation antipsychotic medications.
