Mirtazapine has significant advantages in response and remission rates compared with various SSRIs in double-blind treatment. Mirtazapine combined with SSRIs or venlafaxine was also found to be one of the more effective and successful strategy for nonresponders in MDD. The investigators hypothesized that mirtazapine as adjunctive treatment to paroxetine can boost the onset time and also can improve the antidepression action of SSRIs in patients without early improvement.