Investigating the Effect of Vortioxetine in Adult ADHD Patients

The study employed the Sequential Parallel Comparison Design (SPCD), a clinical study design which intend to increase signal detection by using two stages of treatment: * Stage 1 - first 6 weeks of the 12-weeks treatment period (Visit 2/Baseline 1 to Visit 5/Week 6) * Stage 2 - last 6 weeks of the 12-weeks treatment period (Visit 5/Baseline 2 to Visit 8/Week 12) In Stage 1, patients were randomized to placebo or vortioxetine 10 or 20mg. Patients on vortioxetine 10 or 20mg/day during Stage 1 remained on the same treatment in Stage 2. Responders to placebo in Stage 1 remained on Placebo in Stage 2. Patients who were placebo non-responders during Stage 1, defined as patients with a \<30% reduction in AISRS total score from Baseline 1, were re-randomized to placebo or vortioxetine 10 or 20mg/day in Stage 2.