OXT and depressive disorder: Changes in oxytocin and vasopressin systems (theorized to be involved in romantic love, e.g., Fisher, 1998, 2000; Carter, 2017; Walum and Young, 2018) are associated with depression (see Purba et al., 1996; Van Londen et al., 1998; Neumann and Landgraf, 2012; McQuaid et al., 2014).