The risk of diabetes and HbA1c deterioration during antipsychotic drug treatment: A Danish two-cohort study among patients with first-episode schizophrenia.

Background: Antipsychotics increase the risk of developing diabetes, but clinical trials are not generalizable with short follow-up, while observational studies often lack important information, particularly hemoglobin A1c (HbA1c).

Methods: We followed two Danish cohorts with schizophrenia. First, using Danish nationwide registers, we identified all individuals diagnosed with first-episode schizophrenia (FES) between 1999 and 2019 (n = 31,856). Exposure was a redeemed prescription for an antipsychotic, and the outcome was diabetes, defined via hospital-based diagnosis and redeemed prescriptions for glucose-lowering drugs. Adjusted Cox regression calculated hazard rate ratios (HRR). Second, using data from the Central Denmark Region, we identified all individuals diagnosed with FES from October 2016 to September 2022 (n = 2671). Using a within-subject design, we analyzed the change in HbA1c during the 2 years after initiation of specific antipsychotics compared to the 2 years before.

Results: In the nationwide cohort, 2543 (8.0%) individuals developed diabetes (incidence rate = 9.39 [95% CI = 9.03-9.76] per 1000 person-years). Antipsychotics, compared to periods without, were associated with an increased risk of developing diabetes (HRR = 2.04, 95% CI = 1.75-2.38). We found a dose-response association, particularly for second-generation antipsychotics, and different risk rates for specific antipsychotics. In the Central Denmark Region cohort, a total of 9.2% developed diabetes but mean HbA1c levels remained stable at 37 mmol/mol during the 2 years after initiation of antipsychotic medication.

Conclusion: This comprehensive real-world two-cohort study emphasizes that diabetes affects almost 10% of patients with FES. Antipsychotics increase this risk, while HbA1c deterioration requires longer treatment. These findings are important for clinicians and young patients with FES.