Abstract
BACKGROUND: Photobiomodulation (PBM) is a non-invasive therapy increasingly used for pain, inflammation, and tissue repair, yet a comprehensive synthesis of its effectiveness across multiple health outcomes remains lacking. Herein, we aimed to systematically assess the clinical effects and strength of evidence for PBM across a wide range of health outcomes using data from existing meta-analyses of randomized controlled trials (RCTs). METHODS: We conducted an umbrella review of meta-analyses of RCTs, searching five databases up to December 8, 2023. Two reviewers independently assessed methodological quality using AMSTAR 2 and evaluated certainty of evidence using a modified GRADE framework. Pooled effect sizes were recalculated as equivalent standardized mean differences (eSMD) with 95% confidence intervals (CI). The study was registered with PROSPERO (CRD42023495502). RESULTS: A total of 15 meta-analyses encompassing 204 RCTs and over 9000 participants were included, covering 35 health endpoints across 15 disease conditions. PBM showed significant effects for 12 outcomes, with moderate certainty of evidence supporting improvements in burning mouth syndrome (pain reduction, eSMD - 0.92 [95% CI - 1.38 to - 0.46]), knee osteoarthritis (disability, 0.65 [0.14 to 1.15]), fibromyalgia (fatigue, 1.25 [0.63 to 1.87]), androgenetic alopecia (hair density, 1.32 [1.00 to 1.63]), and cognitive function (0.49 [0.14 to 0.84]). Most other outcomes exhibited low or very low certainty due to heterogeneity or small-study effects. P-curve and funnel plot analyses indicated evidential value for several outcomes, though potential publication bias was identified in some. CONCLUSIONS: PBM appeared beneficial for some health conditions, such as the strongest support for fibromyalgia, osteoarthritis-related disability, and cognitive impairment. However, given the overall low-to-moderate certainty of evidence for most endpoints, further high-quality trials and standardization of PBM protocols are warranted before widespread clinical adoption.