HTR5A and major depressive disorder: The receptor subfamilies for 5-HT contain at least 14 members (Zmudzka et al., 2018), of which the 5-HT1 and 5-HT2 subfamilies are consistently linked to the emergence of neuropsychiatric disturbances and psychological disorders, including major depressive disorder (MDD) and altered social function (Carhart-Harris and Nutt, 2017; Walsh et al., 2018a; Zmudzka et al., 2018).