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Central Neurology and Cognition
Published on
August 31, 2026

Mariano J et al. - Photobiomodulation and Motor Symptoms of Parkinson's Disease: A Systematic Review and Meta-Analysis

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This systematic review with meta-analysis concludes that photobiomodulation is safe and well tolerated in Parkinson’s disease, but that the current evidence does not support a clinically significant motor benefit. The meta-analyses showed no significant effect on the motor score or on the timed walk test.

What this study measured

The authors sought to evaluate the efficacy and safety of photobiomodulation on the motor symptoms of Parkinson’s disease, a progressive neurodegenerative disorder that causes significant motor impairment. Photobiomodulation is defined here as red or near-infrared light applied noninvasively, which had shown promising results in preclinical studies.

This is a systematic review conducted in accordance with the PRISMA guidelines, registered in advance with PROSPERO. Databases were searched through May 2026. Randomized and non-randomized trials conducted in adults with Parkinson’s disease were eligible. Two reviewers worked independently, and random-effects meta-analyses were performed when the data allowed.

Key Findings

Eight trials, involving 279 participants, were included. They were highly heterogeneous: wavelengths, device types, stimulation sites, and light doses varied from one study to another. The authors report that the treatment was safe and well tolerated, with only minor adverse effects.

  • MDS-UPDRS-III motor score (meta-analysis of four randomized trials): mean difference of -1.37 points, 95% CI from -5.55 to 2.80, not statistically significant.
  • Timed Up and Go (TUG) walking test (four randomized trials): mean difference of -0.52 s, 95% CI from -5.03 to 3.99, not significant.
  • TMWT Timed Walking Test (exploratory analysis of two studies): mean difference of -0.65 s, 95% CI from -1.78 to 0.49, with results consistently favoring photobiomodulation.
  • Individual effect sizes: ranging from negligible (d = 0.03 to 0.06) to small to moderate (d = 0.41).

All confidence intervals include the value zero.

How photobiomodulation works for this indication

The article’s abstract does not describe any specific mechanisms. It merely states that photobiomodulation had shown promise in preclinical models, while its clinical efficacy remained uncertain.

Above all, the authors highlight the lack of biomarkers indicating target engagement: the trials do not allow for verification that the light produces the expected biological effect.

Limits You Should Know

The main limitation is the lack of demonstrated benefit: the meta-analyses of the MDS-UPDRS-III and the TUG are not statistically significant, and the confidence intervals are wide, leaving open the possibility of a null, negative, or positive effect. The TMWT analysis is exploratory (two studies).

The authors also point out several structural weaknesses: highly heterogeneous protocols (wavelengths, devices, stimulation sites, dosimetry), small sample sizes, and the absence of biomarkers to confirm target engagement. The abstract does not specify the duration of treatment or follow-up; therefore, these factors are not discussed here.

What This Means in Practice

For a person with Parkinson's disease, this review does not support considering photobiomodulation as an option for improving motor symptoms. However, it does indicate that the technique has been deemed feasible, acceptable, and safe.

The authors call for larger, standardized trials. In the meantime, photobiomodulation is not a substitute for neurological follow-up or prescribed treatment. Any personal course of action should be discussed with a neurologist or primary care physician.

Frequently Asked Questions

Does photobiomodulation improve the motor symptoms of Parkinson's disease?

This meta-analysis did not demonstrate this. Across four randomized trials, the mean difference in the MDS-UPDRS-III score was -1.37 points, with a confidence interval of -5.55 to 2.80, which is not statistically significant. The authors conclude that the current evidence does not support a clinically significant motor benefit.

Is photobiomodulation safe for people with Parkinson's disease?

The authors report that photobiomodulation was safe and well tolerated across all of the included studies, with only minor adverse effects. The abstract does not specify the nature of these effects.

Why are the results of studies difficult to interpret?

Protocols vary greatly from one trial to another: wavelength, type of device, areas stimulated, and light dose. The sample sizes are small, and there are no biomarkers to confirm that the target has been reached.

Reference

Mariano J, Piña Mojica E, Soto-Rodríguez A, Gianlorenço AC, Pacheco-Barrios K, Fregni F. Efficacy and Safety of Photobiomodulation Therapy for Motor Symptoms in Parkinson’s Disease: A Systematic Review and Meta-Analysis. Brain Sciences, 2026;16(9). PMID 42793350. DOI 10.3390/brainsci16090925. https://pubmed.ncbi.nlm.nih.gov/42793350/

This summary is provided for informational purposes only and does not constitute medical advice. Photobiomodulation is not a substitute for prescribed treatment. Consult a healthcare professional.