The crucial difference between vilazodone versus pindolol augmentation is that the latter is a full antagonist whereas the former is a potent partial agonist (Hughes et al., 2005; Khan, 2009), as is aripiprazole (Stahl, 2001) thus permitting activation of post-synaptic 5-HT1A receptors (discussed further in Section “A Psychopharmacological Approach to Treatment-Resistant Depression”). Here, HTR1A is linked to major depressive disorder.