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Evidence Based Longevity (EBL)
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In plain terms

In plain terms: Transcranial Photobiomodulation shows early signals in human research but the evidence is limited -- small trials, surrogate endpoints, or not yet independently replicated. It is an emerging area, not yet a proven one.

Transcranial Photobiomodulation

C Limited: small, mixed or unreplicated trials
Category Devices
Evidence Systematic review of randomized trials
Reviewed July 2026
PMIDs 37843594
The endpoint this grade is based on: Objectively measured functional outcome

The evidence as the record states it

Evidence record
PMID 37843594

Gao et al. (Lasers in Medical Science, 2023; PMID 37843594): systematic review of photobiomodulation for age-related cognitive impairment. Grade C: early, heterogeneous trial evidence.

PMID 37843594

Why Grade C and not Grade B

Grade C reflects early or limited human evidence -- small trials, surrogate endpoints, or preliminary findings not yet independently replicated. The evidence points in a promising direction but does not yet meet the standard for Grade B. A single well-powered, independently replicated trial with a meaningful endpoint would move this to Grade B or higher.

What this grade covers and what it does not

Grade C on cognition. A systematic review and meta-analysis of photobiomodulation for age-related cognitive impairment found early, heterogeneous trial evidence (Gao et al., 2023; PMID 37843594); the strongest recent work remains preclinical. WHAT THIS GRADE DOES NOT COVER: dementia prevention, healthy adults, and any specific device or wavelength, none of which the cited review graded, and the preclinical findings, which carry no letter.

What would move this grade

A well-powered randomized trial with an objective, clinically meaningful primary endpoint and at least one independent replication would support Grade B or higher.

How to track whether this is working A validated cognitive battery (MoCA, CNS Vital Signs) at baseline and 8 weeks. For depression applications, use the PHQ-9 or HAMD-17 at baseline and 8 weeks. Device parameters (wavelength, power output, treatment site, session duration) at every session: transcranial PBM device specifications vary enormously and the literature is not yet protocol-standardized.