The aim of this study is to provide physicians with further information regarding early improvement and mirtazapine combined with a SSRI antidepressant therapy in nonresponders, by providing a comparison of depressive symptoms outcomes associated with adjunctive mirtazapine or mono- paroxetine in MDD patients who have previously been treated with paroxetine for 2 weeks and who have not attained improvement. Paroxetine has been chosen as a comparator because it is a widely-used and relatively well-tolerated SSRI antidepressant.