Inclusion Criteria:  Have a DSM-5 (American Psychiatric Association) diagnosis of schizophrenia Are resistant to adequate treatments of at least two antipsychotics Remain symptomatic but without clinically significant fluctuation, while their antipsychotic doses are unchanged for at least 3 months and will be maintained during the period of the 12-week trial PANSS total score ≥ 70 Agree to participate in the study and provide informed consent  Exclusion Criteria:  DSM-5 diagnosis of intellectual disability or substance (including alcohol) use disorder History of epilepsy, head trauma, stroke, or serious medical or central nervous system diseases (other than schizophrenia) which may interfere with the study Clinically significant laboratory screening tests (including blood routine, biochemical tests) Pregnancy or lactation Inability to follow protocol