Introduction: Clozapine is an antipsychotic agent used in schizophrenia recurrence or when other antipsychotics are not effective. Aims: This study aims to determine the therapeutic outcome and adverse drug reactions of clozapine in schizophrenia disorder among hospitalised patients. Methods: A retrospective cross-sectional study was conducted between January 2018 and December 2019 using inpatients’ medical records from the Grhasia Psychiatric Hospital, Yogyakarta. The therapeutic outcome was measured with the PANSS-EC scale, while adverse drug reactions of clozapine were analysed theoretically as per the literature. Results: The average decrease in the PANSS-EC score was 8.27, and the average duration to achieve this decrease was 2.5 days. The combination of typical-atypical antipsychotics could reduce the highest PANSS-EC score of 11-15 (41%). The adverse drug reactions of clozapine were tremor, weight gain, obesity, leucopenia, hyperglycemia, and hypercholesterolemia, among other effects. Conclusion: Clozapine is effective in improving positive and negative symptoms, but its use needs close monitoring.