BDNF and major depressive disorder: In addition to these results, Almeida et al. (2019) tried to uncover the role between the depression-mitigating effects of ayahuasca and serum BDNF levels [160], given this neurotrophic factor’s potential role as a biomarker in depression: serum BDNF levels in patients with depression are lower than average and increase after treatment with serotonergic antidepressant [161,162].