Portable transcranial direct current stimulation devices promise treatment for depression at home, at scale, for people who cannot access therapy. This systematic review pooled 12 studies, of which six were randomised sham-controlled trials contributing to meta-analysis.
Active home-based tDCS produced a small but statistically significant improvement over sham (Hedges g 0.36, 95% CI 0.06-0.66, I-squared 34.3%). That result did not survive removal of the single largest positive trial (g 0.39, 95% CI -0.12 to 0.91). Trial-level results conflicted: the two largest trials, one unsupervised with 210 participants and one self-administered with 141, were both negative on their primary outcomes, while the largest real-time supervised trial, with 174, was positive. The pooled effect fell at or near the minimal clinically important difference. Adverse events were mostly mild, though one pilot stopped early for skin lesions and one non-fatal suicide attempt occurred in an unsupervised trial.
The review's own conclusion is the right one: current data do not support routine adoption. Note particularly that the evidence does not establish supervision intensity as the determinant of efficacy, despite the tempting pattern — that inference rests on comparing across trials that differ in many other ways too. For a patient asking about a device they have seen advertised, the honest answer is that the effect is small, inconsistent, and not yet established.
- Pooled effect small (Hedges g 0.36) and at the minimal clinically important difference
- Not robust to removing the single largest positive trial
- The two largest trials were negative on their primary outcomes
- One non-fatal suicide attempt in an unsupervised trial
The statistics, in plain English
A pooled result that collapses when one study is removed is the clearest possible sign of fragility: it means the conclusion rests on that trial rather than on the accumulated evidence. Hedges g of 0.36 is a small effect even taken at face value, and the review notes it sits at the threshold of what a patient would notice. The two largest trials being negative while the pooled estimate is positive should make anyone cautious.
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