A systematic review of transcranial direct current stimulation (tDCS) for adults with attention deficit/hyperactivity...

Transcranial direct current stimulation (tDCS) has been proposed as a potential non-pharmacological intervention for Attention-Deficit/Hyperactivity Disorder (ADHD). While evidence from pediatric populations is growing, the effects of tDCS in adults with ADHD remain insufficiently characterized, increasing recognition of ADHD as a lifelong neurodevelopmental condition with persistent functional impairments.

This systematic review aimed to evaluate the effects of tDCS in adults with ADHD across clinical, cognitive, and neurophysiological outcome domains.

Six electronic databases were systematically searched to identify peer-reviewed controlled trials evaluating tDCS interventions in adults with clinically diagnosed ADHD through May 2025. Data extraction encompassed clinical symptom outcomes, cognitive task performance, neurophysiological findings, adverse events, medication status, and stimulation protocols. Study quality was assessed using the Downs and Black checklist. Where sufficient data were available, an exploratory random-effects meta-analysis was conducted for clinical symptom outcomes; all other outcomes were synthesized narratively.

Eleven controlled studies (n = 415) met inclusion criteria and were included in the qualitative synthesis. Two randomized controlled trials provided sufficient data for exploratory meta-analysis of clinical symptoms. Pooled results suggested a possible beneficial effect of tDCS on inattention symptoms, accompanied by substantial heterogeneity (I² = 79.95 %), while no significant effect was observed for hyperactivity/impulsivity. Cognitive outcomes were heterogeneous and domain-specific, with some evidence of post-stimulation improvements in inhibitory control, working memory, and attentional measures. Two studies reported tDCS-induced modulation of frontal neurophysiological markers associated with cognitive control. Stimulation protocols varied considerably across studies, with no consistent association between specific parameters and outcomes. Adverse events were generally mild and transient, and follow-up data were limited.

Current evidence suggests that tDCS may exert domain-specific effects on inattention and selected cognitive functions in adults with ADHD. However, conclusions remain tentative due to methodological heterogeneity, small sample sizes, and limited quantitative evidence. Future research should prioritize standardized protocols, adequately powered trials with extended follow-up periods, integration of neurophysiological biomarkers, and systematic evaluation of individual difference factors to clarify the therapeutic potential and mechanisms, and advance precision neuromodulation approaches for adult ADHD.