Sex Differences in NMDA-enhancing Treatment of Schizophrenia

Inclusion Criteria: * Have a Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) diagnosis of schizophrenia * keep stable mentally for ≥ 6 months before baseline and meet the following clinical criteria: predominantly negative symptoms for ≥ 6 months, a minimum baseline total score of 40 on the SANS, a minimum baseline score of 24 on the negative subscale of the PANSS, and a maximum score of 3 on each item of PANSS-positive subscale; * Are physically healthy and laboratory assessments (including blood routine, biochemical tests) are clinically insignificant; * Have been keeping a fixed dose of antipsychotics for at least 6 months, and that is not allowed to change during the 12-week study period * Have sufficient education to communicate effectively and are capable of completing the assessments of the study * Agree to participate in the study and provide written informed consent Exclusion Criteria: * DSM-5 diagnosis of intellectual disability or substance (including alcohol) use disorder * History of epilepsy, head trauma, or serious medical or central nervous system diseases (other than schizophrenia) which may interfere with the study * Clinically evident depressive symptoms or a baseline score\>7 on the Hamilton Depression Rating Scale-17 items * Clinically relevant parkinsonism or a baseline score \>3 on the sum of the first eight items of the Simpson-Angus Scale (SAS) * Pregnancy or lactation * Inability to follow protocol