SLC18A2 and major depressive disorder: In 2017, the U.S. Food and Drug Administration (FDA) approved valbenazine, an inhibitor of vesicular monoamine transporter 2 (VMAT2), for the treatment of TD; however, the use of VMAT2 inhibitors might cause grave adverse events, such as depression and suicidality (Khorassani et al., 2020).