Transcranial direct current stimulation (tDCS) has been investigated for the treatment of major depressive disorders in recent years. Here, we review the implications of current research for the clinical use of tDCS in the treatment of major depressive disorder. Meta-analyses, randomized, placebo-controlled clinical trials, open-label trials, case reports and review articles were identified through a systematic search of the literature database of the National Institutes of Health (USA). Available articles were evaluated with regard to their clinical relevance. Results of tDCS efficacy are inconsistent due to the small sample sizes, the heterogeneous patient samples and the partially high treatment resistance in some studies. Overall, tDCS has very low side effects. Meta-analyses suggest some efficacy of tDCS in the treatment of acute depressive disorder with moderate effect size, and low efficacy in treatment-resistant depression. A general statement about the efficacy of tDCS as a therapeutic tool in major depression seems to be premature. tDCS is considered as a safe therapeutic option and is associated with only minor side effects. The effectiveness of tDCS decreases with resistance to treatment. Psychotropic drugs may attenuate or amplify its effects. The use of 2 mA current strength over 20 min per day over a short time span can be considered as safe.
Keywords: Major depressive disorder; Noninvasive brain stimulation; Treatment resistance; tDCS.