This multi-centre study will follow a randomised, double-blind, parallel-group, active-controlled design and will evaluate the efficacy, safety and tolerability of bupropion extended-release (XL) (300 mg/day) compared with escitalopram (10-20 mg/day) in outpatients and inpatients with major depressive disorder (MDD). The total duration of the study will be 11 weeks consisting of three phases. The screening phase (phase I) will be lasting for 0-14 days, subjects will be randomised to bupropion XL or escitalopram in a 1:1 ratio for acute phase treatment phase (phase II) for 8 weeks. There are 3 dose levels during this acute treatment phase. The 3-dose level plan is designed to ensure each drug is titrated according to the prescribing information and to reach an optimal clinical dose. Finally patients will enter the taper phase (phase III) for up to 1 week to assess and reduce the possible withdrawal symptoms.