Iron Supplementation on Treatment-Resistant Depressed Patients with Iron-Deficiency: a Randomized, Double-Blind, Placebo-Controlled Study

INTERVENTION: Ferrochel Iron Bisglycinate as add‐on therapy Placebo as add‐on therapy CONDITION: Depression PRIMARY OUTCOME: Change in total score of the Hamilton Depression Rating Scale 17 items(HDRS17) between baseline and endpoint (12 weeks); ; cf. Primary outcomes changed from BDI‐II to HDRS17 on 2018.7.20.; The reason of this change is that HDRS17 may more suitable for the accessment of depression symptoms than BDI‐II INCLUSION CRITERIA: 1) Diagnosed as a depression (DSM‐5) 2) [Criteria for Treatment‐Resistant Depressed Patient] Treated with at least two anti‐depressants for 4 weeks or more, respectively 3) Between 18 and 65 years old 4) Serum ferritin < 25 ng/ml 5) Total score of HDRS17 at baseline >= 14 6) Providing an informed consent