In addition, reserpine (RSP), an irreversible competitive inhibitor of VMAT-2 and VMAT-1 enzymes (Henry and Scherman, 1989), had been used to treat hypertension, and shortly after its introduction, it was withdrawn due to its frequent side effects (depression and parkinsonism) occurring during its application in medical practice. This evidence concerns the gene SLC18A2 and major depressive disorder.