Dual Modulation of Sigma-1 and NMDA Receptors in the Treatment of Schizophrenia

Inclusion Criteria: * Have a DSM-5 (American Psychiatric Association) diagnosis of schizophrenia * Are resistant to adequate treatments of at least two antipsychotics (excluding clozapine) * 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 8-week trial * PANSS total score \>70 * Hamilton Depression Rating Scale-17 items (HAMD) \<7 * Are physically healthy and laboratory assessments (including blood routine, biochemical tests) are clinically insignificant. * Have sufficient education to communicate effectively and are capable of completing the assessments of the study. * 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, central nervous system diseases or mental disorders other than schizophrenia (including major depressive disorder, bipolar disorders, persistent depressive disorder, obsessive-compulsive disorder) * Pregnancy or lactation * Inability to follow protocol