Early changes of serum BDNF and SSRI response in adolescents with major depressive disorder.

•Serum BDNF levels did not differ between medication free/naïve MDD adolescents and healthy controls.•Pre-treatment BDNF levels were not associated with SSRI response in MDD adolescents.•Responders showed early decrease in BDNF levels at week 2 but non-responders and healthy controls did not.•Early BDNF decrease (baseline – week 2) predicted later SSRI response at week 8.