This study assessed the efficacy, tolerability and safety of vortioxetine versus placebo in adults with recurrent major depressive disorder. This double-blind, randomized, placebo-controlled study included 608 patients [Montgomery–Åsberg Depression Rating Scale (MADRS) total score≥26 and Clinical Global Impression – Severity score≥4]. Patients were randomly assigned (1 : 1 : 1 : 1) to vortioxetine 15 mg/day, vortioxetine 20 mg/day, duloxetine 60 mg/day or placebo. The primary efficacy endpoint was change from baseline in MADRS total score at week 8 (mixed model for repeated measurements). Key secondary endpoints were: MADRS responders; Clinical Global Impression – Improvement scale score; MADRS total score in patients with baseline Hamilton Anxiety Rating Scale ≥20; remission (MADRS≤10); and Sheehan Disability Scale total score at week 8. On the primary efficacy endpoint, both vortioxetine doses were statistically significantly superior to placebo, with a mean difference to placebo (n=158) of −5.5 (vortioxetine 15 mg, P<0.0001, n=149) and −7.1 MADRS points (vortioxetine 20 mg, P<0.0001, n=151). Duloxetine (n=146) separated from placebo, thus validating the study. In all key secondary analyses, both vortioxetine doses were statistically significantly superior to placebo. Vortioxetine treatment was well tolerated; common adverse events (incidence≥5%) were nausea, headache, diarrhea, dry mouth and dizziness. No clinically relevant changes were seen in clinical safety laboratory values, weight, ECG or vital signs parameters. Vortioxetine was efficacious and well tolerated in the treatment of patients with major depressive disorder.