A 12-week, randomized controlled trial (RCT) with parallel grouping design will be conducted to compare the efficacy and safety of different treatments. One hundred and eighty adults diagnosed with major depressive disorder (MDD) with no or poor response to initial antidepressant treatment will be recruited. Then all the patients will be 1:2:2 randomly assigned to different intervention groups including escitalopram, escitalopram plus sulforaphane (SFN) , and escitalopram plus repetitive transcranial magnetic stimulation (rTMS). Clinical symptoms and side-effects will be evaluated or recorded using the 17-Hamilton Depression Rating Scale (17-HDRS), the Hamilton Anxiety Scale (HAMA), side-effects sheet, etc., at Critical Decision Points (CDP) including weeks 2, 4, 8 and 12 after treatment. Blood cell counting, biochemical, and electrocardiogram examination will be performed at weeks 4, 8 and 12 after treatment in order to evaluate the effect of different interventions on the physical condition. In addition, niacin skin flush response and serum markers including nuclear factor erythroid-2-related factor 2(Nrf-2), p-Nrf2, malondialdehyde (MDA), superoxide dismutase (SOD) and erythrocyte glutathion peroxidase (GPX) will be tested at baseline and endpoint. The primary outcome is the reduction rate in 17-HDRS total score from baseline to the end of the study. The secondary outcomes include changes in niacin skin flush response test and levels of serum markers. All the data will be analyzed by SPSS software.

The inclusion criteria are as follows:

1. aged 18-60 years;
2. diagnosed with moderate or severe depressive disorder according to the criteria of the DSM-5;
3. total score of 17-HDRS≥17;
4. never receiving electroconvulsive therapy (ECT)/modified ECT (MECT)/rTMS or other treatments in the past month;
5. no response or poor response (having a reduction of <20% on the total score of the 17-item Hamilton Depression Scale compared with the baseline) to adequate antidepressants (except escitalopram) treatment for at least 4 weeks;
6. having sufficient audio-visual ability and comprehension;
7. signed informed consent statements.

The exclusion criteria are as follows:

1. serious or active somatic illness (abnormal index values were more than twice the limit of normal);
2. a history of mania/hypomania;
3. current high risk of suicide (score of item 3 of 17-HDRS ≥ 3);
4. pregnant or lactating women, or planning pregnant women;
5. taking immunosuppressants or vitamins recently.