TAC1 and major depressive disorder: Our finding is based on more patients than those of most previous studies29, 30, 31, 33, 34, 35, 37, 38, 40 and rather support unaltered plasma oxytocin levels in schizophrenia, BD, or MDD in a systematic review and meta‐analysis32 or plasma substance P levels in patients with schizophrenia (patient: n = 43 vs control: n = 34)31 and patients with MDD (patient: n = 42 vs control: n = 57).40