Background Transcranial direct current stimulation has shown promising clinical results,

leading to increased demand for an evidence-based review on its clinical effects.

Objective We convened a team of transcranial direct current stimulation experts to

conduct a systematic review of clinical trials with more than 1 session of stimulation

testing: pain, Parkinson’s disease motor function and cognition, stroke motor function and

language, epilepsy, major depressive disorder, obsessive compulsive disorder, Tourette

syndrome, schizophrenia, and drug addiction.

Methods Experts were asked to conduct this systematic review according to the search

methodology from PRISMA guidelines.Recommendations on efficacy were categorized into

Levels A (definitely effective), B (probably effective), C (possibly effective), or no

recommendation. We assessed risk of bias for all included studies to confirm whether

results were driven by potentially biased studies.

Results Although most of the clinical trials have been designed as proof-of-concept trials,

some of the indications analyzed in this review can be considered as definitely effective

(Level A), such as depression, and probably effective (Level B), such as neuropathic pain,

fibromyalgia, migraine, post-operative patient-controlled analgesia and pain, Parkinson’s

disease (motor and cognition), stroke (motor), epilepsy, schizophrenia, and alcohol

addiction. Assessment of bias showed that most of the studies had low risk of biases, and

sensitivity analysis for bias did not change these results. Effect sizes vary from 0.01 to 0.70

and were significant in about 8 conditions, with the largest effect size being in

postoperative acute pain and smaller in stroke motor recovery (nonsignificant when

combined with robotic therapy).

Conclusion All recommendations listed here are based on current published PubMed-

indexed data. Despite high levels of evidence in some conditions, it must be underscored

that effect sizes and duration of effects are often limited; thus, real clinical impact needs to

be further determined with different study designs.

Key Words tDCS, clinical evidence, evidence-based medicine, neurological disorders,

psychiatric disorders.