Long-term safety, tolerability, and efficacy of adjunctive edivoxetine hydrochloride (hereafter edivoxetine), a highly selective and potent norepinephrine reuptake inhibitor, was assessed in patients with major depressive disorder (MDD) experiencing partial response to selective serotonin reuptake inhibitor treatment. Data are from a multicenter, 54-week, open-label trial of adjunctive edivoxetine 12 to 18 mg once daily in patients with MDD who had experienced partial response by history to 6 or more weeks of current selective serotonin reuptake inhibitor therapy and who had a 17-item GRID Hamilton Rating Scale for Depression total score 16 or higher at study entry. Safety measures included discontinuation rate, treatment-emergent adverse events, serious adverse events, and vital signs. Efficacy measures included the Montgomery-Åsberg Depression Rating Scale. Of 608 patients, 328 (54%) completed the open-label adjunctive treatment. Study discontinuation due to adverse events occurred in 17.0%, and there were 13 serious adverse events (1 death). Treatment-emergent adverse events 5% or higher were nausea, hyperhidrosis, constipation, headache, dry mouth, dizziness, vomiting, insomnia, and upper respiratory tract infection. Mean increases were observed in systolic blood pressure (range, 0.0-2.3 mm Hg), diastolic blood pressure (range, 1.9-3.3 mm Hg), and pulse (range, 5.9-8.4 beats per minute). Mean improvements on the Montgomery-Åsberg Depression Rating Scale (-17.0) were observed from baseline to week 54. The safety profile from this study provides an overview of outcomes associated with edivoxetine and norepinephrine reuptake inhibition as an adjunctive treatment in patients with MDD who were treated up to 1 year.