Participants

All participants met the following criteria: (1) male or female patient aged 18–65 years; (2) had a diagnosis of MDD without psychotic symptoms according to the Diagnostic and Statistical Manual of Mental Disorders, fifth edition (DSM-V); (3) scored ≥17 on the 17-item Hamilton Depression Rating Scale³⁵; (4) had a history of either TRD (history of nonresponse to two or more adequate antidepressant treatment trials) or suicidal ideation (Beck Scale for Suicide Ideation-part I ≥2); (5) able to understand and complete the study procedure; and (6) signed an informed consent form before participating in the program.

Subjects in the following circumstances were excluded: (1) diagnosed with bipolar depression (BD I/BD II); (2) had a current or previous diagnosis of any other severe mental disorder according to the Structured Clinical Interview for DSM-V (i.e., schizophrenia or organic mental disorders); (3) had a history substance abuse or dependence except for nicotine; (4) had a positive urine toxicological screening; (5) had a major medical illness (i.e., a serious and unstable physical disease, chronic inflammatory illness, or autoimmune disease); (6) was being treated with a combination of anti-inflammatory agents (i.e., nonsteroidal anti-inflammatory drugs or steroids); (7) was pregnant or was preparing for pregnancy or lactation; (8) was unable to carry out the study procedures.