Electroconvulsive therapy, BDNF and major depressive disorder: A meta-analysis with biological subgroups and clinical assessment of outcomes

Electroconvulsive therapy (ECT) proves to be an effective intervention in severe cases of major depressive disorder (MDD), especially when there is resistance to pharmacological treatment. The neurotrophic hypothesis proposes that an increase in brain-derived neurotrophic factor (BDNF) is one of the mechanisms responsible for the therapeutic response. The aim of this study is to investigate the effects of ECT on peripheral levels of BDNF, measured in serum and plasma, and analyze clinical outcomes associated with this intervention, as well as identify methodological variables that may influence findings. A systematic review and meta-analysis of studies published between 1995 and 2025 on the PubMed, Scopus and Web of Science databases were conducted, following Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines. Studies of BDNF in serum (14) and plasma (6) were performed separately. Clinical effectiveness was evaluated according to average standardized differences in depression scores. Meta-regressions in the R software identified the impact of four moderators: type of ECT, number of sessions, type of anesthetic and the time blood sample was taken. ECT was associated with an increase in BDNF levels in both biological matrices, especially in studies with plasma (I² = 0%). Significant reductions in depression symptoms were also observed. These meta-regressions indicate that the kind of anesthetic used and the time the blood sample was taken greatly influence BDNF levels. The biological matrix used, as well as specific methodological variables, affects the measurement of BDNF, reinforcing the need to standardize future studies.