Additionally, catalpol and geniposide are two representative iridoids in Cistanches Herba, and they have been found to ameliorate chronic unpredictable stress (CUS)-induced depression-like behavior via restoring hypothalamic–pituitary–adrenal (HPA) axis dysfunctions and catalpol can upregulate brain-derived neurotrophic factor (BDNF) expression (Cai et al., 2015; Wang et al., 2015). Here, BDNF is linked to major depressive disorder.