Transcranial direct current stimulation (tDCS) is a non-invasive neurostimulation technique that has received increasing interest in the area of mood disorders over the last several years. While acute, double-blind, sham-controlled studies have already reported positive findings in terms of efficacy and safety for tDCS, follow-up data are lacking. This need prompted the present follow-up study, which assesses post-acute effects of tDCS (no maintenance stimulation was performed), in the mid-term, in a sample of major depressives.

After completing an acute, open trial of tDCS, 23 outpatients with either major depressive disorder or bipolar disorder entered a naturalistic follow-up (T1) with clinical evaluations at one week (T2), 1 month (T3), and 3 months (T4). A quantitative analysis of Hamilton Depression Rating Scale (HAM-D), Montgomery–Asberg Depression Rating Scale (MADRS), and Young Mania Rating Scale (YMRS) total scores, through repeated measures analysis of variance (ANOVA) (T1–T4) and paired t-test for comparing specific time points (T1–T2, T2–T3, and T3–T4), was performed. In addition, a qualitative analysis on the basis of treatment response and remission (HAM-D) was performed.

Even though a progressive reduction of follow-up completers was observed from T2 to T4 (95.6% at T2, 65.2% at T3, and 47.8% at T4), the antidepressant effects of acute tDCS persisted over 3 months in almost half of the sample. Of note, no post-acute side effects emerged during the follow-up observation. The most frequent causes of drop-out from this study included major modifications in therapeutic regimen (30%) and poor adherence to follow-up visits (17%).

In this mid-term, open, follow-up study, tDCS showed mixed results. Further controlled studies are urgently needed to assess its effects beyond the acute phase.