Efficacy of Transcranial Photobiomodulation on Depressive Symptoms: A Meta-Analysis.

Transcranial photobiomodulation (tPBM) is a novel, noninvasive, device-based intervention, which has been tested as a possible treatment for various neurological and psychiatric conditions. Recently, it has been investigated as an innovative treatment for major depressive disorder (MDD). There have been several animal and clinical studies that evaluated the underlying mechanism and the efficacy of its antidepressant effects, but results have been conflicting. Thus, we conducted the first meta-analysis on effects of tPBM on depressive symptoms. Thirty original articles on tPBM were retrieved, eight of them met criteria for inclusion to a random effects meta-analysis. tPBM appeared effective in decreasing depressive symptom severity regardless of diagnosis (Hedges'  = 1.415,  < 0.001,  = 8), but a significant heterogeneity has been found. The meta-analysis of single-arm studies (baseline to endpoint changes) limited to participants with MDD has supported the significant effect of tPBM in reducing the depression severity, without a significant heterogeneity (Hedges'  = 1.142, 95% confidence interval = 0.780-1.504,  = 6.19,  < 0.001,  = 5). However, the meta-analysis of the few double-blind, sham-controlled studies in MDD has not supported the statistically significant superiority of tPBM over sham (Hedges'  = 0.499,  = 0.211,  = 3), although a sample size bias is likely present. Overall, this meta-analysis provides weak support for the promising role of tPBM in the treatment of depressive symptoms. Dose finding studies to determine optimal tPBM parameters followed by larger, randomized, sham-controlled studies will be needed to fully demonstrate the antidepressant efficacy of tPBM.