BDNF and major depressive disorder: We included 20 studies that described comparisons of average BDNF levels pre- and post-antidepressant treatment with SSRIs, SNRIs, TCAs et al. First, we performed systematic meta-analyses and found that subjects with MDD had significantly higher BDNF concentrations after a short-term period (less than 12 weeks) of antidepressants treatment, accompanied by reduced HDRS scores.