Severe hyperglycemia induced by olanzapine was improved with a recovery of insulin secretion after switching to risperidone and introducing insulin therapy.

A 35-year-old woman, diagnosed as schizophrenia and treated with olanzapine for nearly 30 months, consulted our department because of severe hyperglycemia. The use of antipsychotics, switching from olanzapine to risperidone, and a one-month introduction of insulin therapy resulted in the decrease of pre-prandial blood glucose levels and the increase of insulin levels (269 to 128 mg/dL, 5.6 to 21.8 µU/mL). A higher level of insulin resistance as measured by HOMA-IR after the improvement of hyperglycemia (3.6 vs. 6.8) suggested that the long use of olanzapine reduced insulin secretion. Based on this case, impairment of pancreatic β-cells caused by olanzapine might be reversible.