Diagnostic heterogeneity and clozapine use among patients referred for suspected treatment-resistant schizophrenia

Patients referred for suspected treatment-resistant schizophrenia (TRS) may constitute a diagnostically heterogeneous population. We retrospectively studied 392 patients referred to an outpatient service for suspected TRS. Electronic clinical records were reviewed, and patients classified according to ICD-10 after specialist reassessment. Treatment patterns and factors associated with clozapine exposure were examined across diagnostic groups. A substantial proportion of patients were classified outside schizophrenia (F20), particularly as organic psychotic disorders (F06) or unspecified psychosis (F29). Patients with schizophrenia (F20) and schizoaffective disorder (F25) showed higher clozapine exposure and greater antipsychotic burden, whereas F06 and F29 groups showed lower pharmacological intensification. F29 diagnosis was independently associated with lower odds of clozapine exposure compared with F20. Patients referred for suspected TRS are diagnostically and therapeutically heterogeneous. Diagnostic reassessment is important, and clozapine exposure should be interpreted within the diagnostic and treatment context rather than as a stand-alone marker of TRS status.