Effect of photobiomodulation intervention for depressive symptoms: A systematic review and meta-analysis

Although photobiomodulation (PBM) has been investigated as a non-invasive treatment for reducing depressive symptoms, its effectiveness and optimal treatment settings remain unknown. This meta-analysis assessed the overall impact of PBM on depressive symptoms and analyzed significant moderators affecting treatment outcomes.

We systematically reviewed 18 PBM intervention trials including individuals with major depressive disorder or clinically significant depressive symptoms. Effect sizes (Hedges' g) were pooled, and moderator analyses were conducted using meta-regression and subgroup comparisons. Publication bias was assessed with funnel plots and the trim-and-fill method.

PBM showed a moderate overall effect in reducing depressive symptoms (Hedges' g = -0.47, 95 % CI: -0.73 to -0.22). Importantly, systemic PBM (sPBM) demonstrated significantly larger effects than those of transcranial PBM (tPBM), underscoring their distinct mechanistic and methodological profiles. Laser-based PBM was more effective than LED-based PBM, and longer treatment duration was associated with greater therapeutic benefits, whereas irradiance and treatment frequency were not significant moderators.

PBM appears to be a promising treatment option for depressive symptoms. The clear difference between sPBM and tPBM highlights the need for modality-specific optimization and further large-scale trials to establish standardized therapeutic protocols.