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Aim As an emergency measure during the coronavirus disease pandemic, the monitoring interval for clozapine use was temporarily extended beyond the regulatory requirement in Japan, which is the safest monitoring interval worldwide. In this study, we aimed to explore the effect of this measure on patients undergoing clozapine treatment. Methods This retrospective chart review study included patients with treatment‐resistant schizophrenia (TRS) who were undergoing clozapine treatment at four psychiatric institutions in Japan. Demographic characteristics and clinical information of these patients were collected on April 27, 2020, when Japanese psychiatrists were virtually allowed to prescribe clozapine beyond the regulatory requirement. Furthermore, information of adverse events related to the emergency measure was collected and analyzed. Results Of the 41 patients with TRS included in this study, 19 patients underwent extended hematological monitoring during clozapine treatment. No psychiatric or hematological adverse events were observed in the patients during the extended monitoring interval. Conclusion This study suggested that there were few adverse events of clozapine‐treated patients related to emergency measures in Japan. However, hematological monitoring intervals during clozapine treatment have been emergently extended worldwide; hence, it is necessary to verify the results of these measures., This retrospective chart review study explored patients with treatment‐resistant schizophrenia who were undergoing clozapine treatment on the expanded hematological monitoring during the coronavirus disease pandemic in April 2020 at four psychiatric institutions in Japan. This study suggested that there were few adverse events of clozapine‐treated patients related to emergency measures in Japan.