At present, the treatment of Bipolar I disorder (BD-I), especially its depressive episode (bipolar depression), is still limited, because there is no effective treatment for the associated cognitive impairment and perceived stress. NMDA receptor (NMDAR) dysfunction is associated with BD-I, particularly its cognitive impairment and perceived stress. This study aims to examine the efficacy and safety of an NMDA enhancer (NMDAE) in the treatment of cognitive impairment and perceived stress in the patients with bipolar depression.

Bipolar I disorder (BD-I) is a severe brain disorder. At present, the treatment of BD-I, especially its depressive episode (bipolar depression), is still limited, because there is no effective treatment for the associated cognitive impairment and perceived stress. This study aims to examine the efficacy and safety of an NMDA enhancer (NMDAE) in the treatment of cognitive impairment and perceived stress in the patients with bipolar depression.

The subjects are bipolar depression patients. They have been treated for bipolar depression for at least four weeks but remain depressive. Participating in this study, they will continue the original treatment, and will be randomized, double-blindly to receive the NMDAE or placebo for 8 weeks. We will measure 6 cognitive domains (including 9 cognitive tests) and quality of life at weeks 0 and 8; and assess the Perceived Stress Scale, Global Assessment of Function (GAF), various scales for clinical symptoms, and side effects at weeks 0, 2, 4, 6, and 8.

The efficacies of NMDAE and placebo will be compared. Chi-square (or Fisher's exact test) will be used to compare differences of categorical variables and t-test (or Mann-Whitney test if the distribution is not normal) for continuous variables between treatment groups. Mean changes from baseline in repeated-measure assessments will be assessed using the generalized estimating equation (GEE). All p values for clinical measures will be based on two-tailed tests with a significance level of 0.05.

Inclusion Criteria:

• Are 18 to 65 years of age;
• Satisfy a DSM-5-TR (American Psychiatric Association) diagnosis of BD-I, current episode depressed, after treatment of stable (i.e., at least 4 weeks) and adequate treatment of antipsychotic (quetiapine or lurasidone) and/or mood stabilizer;
• Have a 17-item Hamilton Depression Rating Scale (HAMD) score ≥18 and a Young Mania Rating Scale (YMRS) score ≤7 at baseline;
• Agree to participate in the study and provide informed consent

Exclusion Criteria:

• Current substance abuse or history of substance dependence in the past 6 months
• History of epilepsy, head trauma, stroke or other serious medical or neurological illness which may interfere with the study
• Schizophrenia or other psychotic disorder
• Moderate-severe suicidal risks
• Severe cognitive impairment
• Clinically significant laboratory screening tests (including blood routine, biochemical tests)
• Pregnancy or lactation;
• Inability to follow protocol