OXT and major depressive disorder: The neuropeptide oxytocin (OXT) has long been known to play a pivotal role in the regulation of complex social cognition and behaviors, including prosocial behavior and pair-bonding (Heinrichs et al., 2009; Galbally et al., 2011; Odent, 2013) as well as in emotional behavior including anxiety and depression (Neumann and Landgraf, 2012; Jurek and Neumann, 2018; Onaka and Takayanagi, 2019; Yoon and Kim, 2020).