A serotonin-norepinephrine reuptake inhibitor (SNRI) or SSRI is widely used as a first-line therapeutic, but 55–81% older persons with major depressive disorder (MDD) fail to recover due to treatment resistance (Lenze et al., 2015) and SSRIs also had to discontinue because of inhibiting gut motor via 5-HT2 receptor and acyl ghrelin (Fujitsuka et al., 2009). This evidence concerns the gene HTR2A and major depressive disorder.