BDNF and psychiatric disorder: Its levels are reduced in patients with several psychiatric disorders, but it is unclear if the response to psychotherapy can alter its concentration.<h4>Objective</h4>To carry out a systematic review evaluating the effects of individual psychotherapy in BDNF levels in patients with mental disorders.<h4>Methods</h4>The databases PubMed, EMBASE, PsycArticles, SciELO, Web of Science, and CENTRAL; the last search was performed on October 2019 for trials evaluating the effects of individual psychotherapy in BDNF levels in adults with mental disorders.