Ji Q. et al. - Photobiomodulation Improves Symptoms of Depression: A Systematic Review and Meta-Analysis

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A meta-analysis published in *Frontiers in Psychiatry* includes 11 randomized trials and reports a moderate reduction in depressive symptoms following photobiomodulation (SMD -0.55; 95% CI -0.75 to -0.35). No significant effect was observed on sleep, and the quality of the evidence is considered moderate to very low.

What this study measured

Qipei Ji’s team searched ten databases, covering the period from their inception through September 25, 2023, and selected only randomized controlled trials focusing on depression. Of the 3,265 references identified, eleven trials were included in the quantitative analysis. The primary outcome measure was the severity of depressive symptoms; the secondary outcome measure was sleep. The authors distinguished between two treatment modalities: transcranial photobiomodulation (t-PBM) and systemic photobiomodulation (s-PBM). The certainty of the evidence was assessed using the GRADE method, and the protocol was registered with PROSPERO.

Key Findings

The overall effect on depression is statistically significant but of moderate magnitude. The result regarding sleep, however, does not reach the significance threshold.

Depressive symptoms: standardized mean difference of -0.55 (95% CI -0.75 to -0.35), I² heterogeneity of 46%.
Sleep: standardized mean difference of −0.82 (95% CI −2.41 to 0.77), I² of 0%, result not significant (p > 0.05).
Eleven included trials, selected from 3,265 references.
In the subgroups, the systemic route was found to be superior to the transcranial route.
Transcranial parameters associated with the best results: 823 nm, fluence of 10 to 100 J/cm², irradiance of 50 to 100 mW/cm², 30 minutes of irradiation, fewer than 3 sessions per week, more than 15 sessions in total.
Systemic parameters associated with the best results: 808 nm, fluence of 1 J/cm² or less, irradiance of 50 to 100 mW/cm², treatment duration of 5 minutes or less, at least 3 sessions per week, and more than 15 sessions in total.
The certainty of the evidence was judged to be moderate to very low, with no publication bias detected.

How Transcranial Photobiomodulation Works

The proposed mechanisms remain hypothetical. Red and near-infrared light is thought to be absorbed by cytochrome c oxidase, an enzyme in the mitochondrial respiratory chain, thereby increasing the production of ATP available to neurons. Other mechanisms are discussed in the literature: modulation of local cerebral blood flow, reduction of oxidative stress, and attenuation of neuroinflammation. These findings are based on preclinical studies and were not measured in this meta-analysis, which focuses on clinical scores.

Limits You Should Know

The number of available trials remains low, as the authors themselves point out. The certainty of the evidence is rated as moderate to very low according to GRADE, which limits the scope of the conclusions. The effect on sleep is not statistically significant, and its very wide confidence interval reflects a high degree of imprecision. The 46% heterogeneity on the primary outcome suggests that protocols, study populations, and devices differ across trials. Finally, the findings identified in subgroups are based on few studies and require confirmation.

What This Means in Practice

This study describes a positive effect on depressive symptoms, but it does not establish a standard protocol or guarantee individual benefit. Photobiomodulation is not a substitute for psychiatric care or ongoing treatment: a mood disorder requires professional support. Any course of action should be discussed with the treating physician, as a supplement to the established treatment plan and never as a replacement for it.

Frequently Asked Questions

Does photobiomodulation reduce the symptoms of depression?

This meta-analysis reports a moderate reduction in depression scores in the included trials. The effect size remains moderate, and the certainty of the evidence is limited. This represents a research finding and does not constitute established efficacy at the individual level.

How many sessions were included in the protocols analyzed?

The most effective subgroups included a total of more than 15 sessions. The frequency varied by treatment modality: fewer than 3 sessions per week for transcranial treatment, and at least 3 per week for systemic treatment. These values describe published protocols and do not constitute a recommendation.

Does photobiomodulation improve sleep in people with depression?

Not in this analysis. The result regarding sleep was not statistically significant, and its confidence interval was very wide. The authors advise against drawing any conclusions based on this criterion.

Reference

Ji Q, Yan S, Ding J, et al. Photobiomodulation improves depression symptoms: a systematic review and meta-analysis of randomized controlled trials. Frontiers in Psychiatry, 2024; 14: 1267415. PMID 38356614. DOI 10.3389/fpsyt.2023.1267415. https://doi.org/10.3389/fpsyt.2023.1267415

This summary is provided for informational purposes only and does not constitute medical advice. Photobiomodulation is not a substitute for prescribed treatment or psychiatric care. Please consult a healthcare professional.