Antidepressant drug therapy is the primary therapeutic treatment option in moderate to severe Major Depressive Disorder. However, clinically significant antidepressant response needs sustained treatment during weeks to months. Indeed, in the largest effectiveness study conducted to date (STAR*D study) involving nearly 3000 depressed outpatients, only about one third of those who ultimately responded did so after 6 weeks of drug treatment and for most patients longer treatment periods were necessary. This delay implies prolonged suffering for the patients and their families. By its antagonist action on the serotonin 1A receptor pindolol is hypothesized to reduce the down-regulation mechanisms of antidepressants. It is therefore expected that addition of pindolol to escitalopram will shorten the therapeutic response. Clinical and preclinical data indicate that escitalopram at 30 mg/day might be more effective and perhaps be associated with a faster onset of action than 20mg. For this purpose the speed of action will be compared between three blindly randomized samples: