Transcranial direct current stimulation combined with cognitive-behavioral interventions for depressive disorders: a systematic review and meta-analysis of sham-controlled randomized trials.

INTRODUCTION: Depressive disorders are a prevalent psychiatric condition; major depressive disorder (MDD) specifically affects approximately 5.7% of adults worldwide and is associated with high levels of disability and disease burden. Although effective interventions are available, some patients do not achieve adequate remission or response rates. In such cases, clinicians often combine interventions to enhance outcomes. This systematic review evaluated whether adding transcranial direct current stimulation (tDCS) to cognitive-behavioral interventions (CBIs) reduces depressive symptoms and improves response and remission rates versus sham tDCS in a sample of patients with depressive disorders. METHODS: We searched ClinicalTrials.gov, Embase, Scopus, PubMed, Web of Science, Cochrane, PsycINFO, and Ovid from inception to October 2025. The primary outcome was reduction in depressive symptoms; response and remission rates were secondary outcomes. Standardized mean difference (SMD) and risk ratio (RR) were used as effect measures for continuous and dichotomous outcomes, respectively, within a random-effects model. Only randomized controlled trials (RCTs) selected according to the PICO framework were included. RESULTS: Ten RCTs comprising 321 patients were included. Primary analysis showed no significance between intervention and control in a sample with MDD as primary diagnosis (SMD: -0.05; 95% CI: -0.44 to 0.34; I² = 26%). Secondary analysis did not demonstrate a significant advantage over the control group for any reported outcome: depressive symptoms (SMD = -0.03; 95% CI -0.30 to 0.23; I² = 6%), response (RR = 1.08; 95% CI 0.67 to 1.74; I² = 0%), or remission (RR = 1.33; 95% CI 0.74 to 2.38; I² = 0%). Subgroup analyses of cognitive behavioral therapy (CBT) and cognitive control training (CCT) also showed no significant advantage. CONCLUSIONS: In sham-controlled trials, current evidence does not demonstrate a reliable incremental benefit of adjunctive tDCS over sham when paired with heterogeneous CBIs in patients with depressive disorders. These findings should be interpreted with caution because of methodological heterogeneity in intervention parameters and insufficient statistical power. SYSTEMATIC REVIEW REGISTRATION: https://osf.io/bf4qt/overview, identifier, 10.17605/OSF.IO/BF4QT.