The purpose of this study is to evaluate the factors affecting the occurrence of adverse drug reactions (glucose and lipid metabolism abnormality, changes in liver function index and sleeping tendency) and clinical effects in schizophrenia patients with clozapine treatment

1. The baseline tests (sleeping tendency assessment, clinical symptom and cognitive assessments, clinical laboratory tests, genotyping, exploratory biomarker tests, etc.) are conducted to the schizophrenia patients before initiation of the clozapine dosing.
2. On day 15 and 57, the changes from baseline clinical symptom and cognitive function are assessed after clozapine treatment. Also, the occurrence of adverse drug reactions are evaluated. In addition, blood sample collections are performed for the assessment of clozapine and its metabolite levels.

Inclusion Criteria:

1. Patients who are diagnosed with schizophrenia spectrum disorder and are expected to use clozapine for more than 57 days to treat or prevent recurrence of schizophrenia
2. Patients who are 19 years or older
3. Patient who understands the contents of the clinical research and provide their written informed consent forms

Exclusion Criteria:

1. Patients taking a drug that the researcher deems inappropriate before clozapine administration
2. Patients who can not use an appropriate contraceptive method during the study period
3. Patients whom the researcher deemed inappropriate for clinical research participation

Patients who are diagnosed with schizophrenia spectrum disorder and are expected to use clozapine for more than 57 days to treat or prevent recurrence of schizophrenia