Depressive disorder, also known as depression, is a type of mood disorder characterized by persistent low mood. The incidence of depression worldwide is about 6%. Growing evidence suggested that the gut microbiota plays a key role in the development of depression. Probiotics can effectively regulate gut microbiota, and showed potential in alleviating depression. This study investigated the effect of formula probiotic (containing Lactobacillus paracasei, Bifidobacterium animalis, Bifidobacterium longum, Bifidobacterium bifidum and Lactobacillus plantarum) on depression.

Inclusion Criteria:

• Normal body mass index ≥ 18.5 until ≤ 29.9
• Mild to moderate major depression diagnosed by psychiatrists according to the diagnostic criteria for depressive episodes in DSM-5 (American Diagnostic and Statistical Manual of Mental Disorders (Fifth Edition))
• Hamilton Rating Scale for Depression (HAMD-17) score not less than 8
• Agreed to intake study product during the study period
• Agreed to sign written informed consent

Exclusion Criteria:

• Use of systemic antibiotics or antimycotics medication in the 30 days prior to the study
• Investigator's uncertainty about the willingness or ability of subject to comply with the protocol requirements
• Persons with a milk protein allergy, lactose intolerance
• Pregnant or breastfeeding women
• Subject had other serious diseases