Transcranial Direct Current Stimulation (tDCS) in Diabetes: A Focused and Mechanistic Review of Symptom and Function Outcomes.

Transcranial direct current stimulation (tDCS) is being explored as an adjunct for diabetes-related symptoms grounded in diabetes-associated alterations in brain networks. We reviewed clinical trials of tDCS conducted in people with diabetes and summarized mechanistic findings relevant to metabolic control. Two reviewers searched PubMed/MEDLINE, Cochrane Library, Google Scholar, Scopus, and ResearchGate for studies published from 1 January 2008 to 31 August 2025. Forty-one records were identified; after screening and full-text assessment, 11 studies met the inclusion criteria. Across predominantly middle-aged adults with long-standing type 2 diabetes, protocols were low-intensity and well-tolerated. The most consistent clinical benefit was analgesia with primary motor cortex stimulation, with randomized comparisons favoring active tDCS over sham. Dorsolateral prefrontal stimulation paired with working-memory training improved cognition and reduced anxiety, while combined motor-prefrontal courses yielded gains in sleep quality and health-related quality of life; a small, randomized study in proliferative diabetic retinopathy reported short-term visual improvements after occipital stimulation. Safety was favorable, and no serious adverse events were reported. Objective metabolic endpoints in diabetic cohorts were scarce; early evidence for insulin-independent improvements in glucose handling and neurometabolic shifts derives mainly from non-diabetic or mixed samples and remains hypothesis-generating. Overall, tDCS appears to be a promising, well-tolerated adjunct for diabetes-related complications. Larger, rigorously sham-controlled trials that align targets with clinical phenotypes and include standardized metabolic outcomes are needed.