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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.

The field of transcranial electrical stimulation (tES) has experienced significant growth in the past 15 years. One of the tES techniques leading this increased interest is transcranial direct current stimulation (tDCS). Significant research efforts have been devoted to determining the clinical potential of tDCS in humans. Despite the promising results obtained with tDCS in basic and clinical neuroscience, further progress has been impeded by a lack of clarity on international regulatory pathways. Therefore, a group of research and clinician experts on tDCS were convened to review the research and clinical use of tDCS. This report reviews the regulatory status of tDCS and summarizes the results according to research, off-label, and compassionate use of tDCS in the following countries: Australia, Brazil, France, Germany, India, Iran, Italy, Portugal, South Korea, Taiwan, and the US. Research use, off label treatment, and compassionate use of tDCS are employed in most of the countries reviewed in this study. It is critical that a global or local effort is organized to pursue definite evidence to either approve and regulate or restrict the use of tDCS in clinical practice on the basis of adequate randomized controlled treatment trials., F.F. is supported by a grant from National Institutes of Health (NIH) (Grant number 1R44NS08063201). A.R.B. is supported by the following grants: 2013 NARSAD Young Investigator from the Brain & Behavior Research Foundation (Grant Number 20493), 2013 FAPESP Young Researcher from the São Paulo State Foundation (Grant Number 20911-5) and National Council for Scientific and Technological Development (CNPq, Grant Number 470904). J.B. is supported by the 2013 NARSAD Young Investigator from the Brain & Behavior Research Foundation (Grant Number 20988). H.E. is supported by grants from Tehran University of Medical Sciences. J.L. (SFRH/BPD/86027/2012) and S.C. (SFRH/BPD/86041/2012) are supported by grants from the Portuguese Foundation for Science and Technology (FCT). C.H.J. is supported by MOST (101-2811-H-008-014). G.V. is supported by as the Department of Science and Technology (Government of India) Research Grant (SR/CSI/158/2012) as well as Wellcome Trust / DBT India Alliance Senior Fellowship Research Award (500236/Z/11/Z). N.B. is supported by a F.A.R. grant from the University of Milano-Bicocca. M.B. is supported by NIH (NINDS, NIMH, NCI), Wallace H Coulter Foundation, Grove Foundation, DoD. W.C. is supported by National Council for Scientific and Technological Development-CNPq WC-301256/2013-6. The group is also grateful to the support from the Conselho Brasileiro de Neuromodulacao Clinica – Instituto Scala.