Previous studies found that some NMDA-enhancing agent was able to augment antioxidant activity and its adjunctive therapy was better than placebo in reducing clinical symptoms and cognitive deficits and revealed favorable safety in patients with chronic schizophrenia. Of note, a substantial portion of schizophrenia patients refuse or cannot tolerate antipsychotics due to poor response or severe side effects. Therefore, this study aims to examine the efficacy and safety of an NMDA enhancer (NMDAE) as a monotherapy for the treatment of schizophrenia.