The secondary objectives of the study are to compare the effects of the three different treatment regimen as assessed by the following variables and, if applicable, by their changes from randomisation to week 6 (end of study). Additionally the time of onset of therapeutic effect will be assessed by evaluating efficacy data after the first four days (Day 4) of treatment as well as after the first week of treatment (Day 8). These analyses will also be performed in the subgroups of patients with 2 failed previous antidepressants and patients with 1 failure.