Moreover, saikosaponin D increases the expression of fibroblast growth factor 2 (FGF2), a growth factor related to neuronal growth and synaptic plasticity that is associated with major depressive disorder (Gupta et al., 2018) (Wu et al., 2017), both in vivo and in vitro, which provided further insight into the anti-depression mechanism of saikosaponin D (Chao et al., 2020). Here, FGF2 is linked to major depressive disorder.