One-Year Clinical Outcomes After Diagnosis According to Early Medication Adherence in First-Episode Schizophrenia: A Nationwide, Health Insurance Data-Based Retrospective Cohort Study

Objectives: Early pharmacologic intervention is considered necessary for improving the prognosis in patients with first-episode schizophrenia (FES). However, few nationwide population-based studies have focused on early medication adherence. We investigated the status of early adherence to antipsychotics and the effect of early adherence on later clinical outcomes in FES.Methods: We used data from the South Korean Health Insurance Review Agency database (2009-2021). We selected 28,931 patients with FES who had a prescription record of at least one antipsychotic medication within 180 days after their diagnosis. We measured early medication adherence using the medication possession ratio (MPR) and compared demographic characteristics and results of psychiatric hospitalization between the adherence group (0.6≤MPR<1.1) and the non-adherence group (MPR<0.6).Results: The average early medication adherence was 0.82 by MPR, and the non-adherence group accounted for 15.6% of all subjects. From 1 to 2 years after diagnosis, the adherence group showed a higher number of psychiatric hospitalizations per hospitalized patient but a shorter duration than the non-adherence group. Additionally, the proportion of patients who experienced psychiatric hospitalizations was smaller in the adherence group.Conclusion: In patients with FES, early medication adherence is associated with lower rates of psychiatric hospitalization and shorter hospitalization durations.