Levomilnacipran is effective clinically in patients with major depressive disorder (MDD) at doses ranging between 40 and 120 mg/day (Asnis et al., 2015). Given this wide effective dose range, it appears essential to determine the in vivo potency of levomilnacipran and the dose at which it starts inhibiting 5-HT in relation to NE reuptake in humans.