8-week of PS128 RCT in Patients With Major Depressive Disorder

The eligible patients will be randomly assigned to either active (PS128) or identical-appearing placebo capsule in an 1 : 1 ratio. A research assistant who is blind to the status of participants will conduct the randomization allocation. Recruited patients will be randomized in 1:1 ratio, by a computer-generated allocation sequence with blocks of 4. Patients, caregivers, and investigators will be all masked to the assignment. To ensure the concealment of the randomization assignment, active drug and placebo will be provided by coded containers. At the end of the first year, the investigators will temporarily decode the blinded medication to analyze the preliminary results. Active capsule containing 300 mg of probiotics, equivalent to 3x10\^10 CFU of Lactobacillus plantarum PS128. PS128 and placebo will be manufactured by BENED biomedical and packed by a GMP pharmaceutical manufacture. PS128 or placebo will be provided twice, in the morning and in the afternoon, daily. Because activity and diet may alter composition of gut microbiota, the investigators will ask eligible patients not to change their lifestyle or diet pattern. In addition, though effects of psychotropics on inflammation are still controversial (Baumeister et al. 2016b), medications will be kept unchanged during the intervention period. If kinds of psychotropic were changed because of worsening clinical condition, the patient will be withdrawal from the study. However, if only dose of psychotropics were change, the investigators will record the changes, and the patients will be still kept in the study.