Therapeutic response to transcranial direct current stimulation (tdcs) in attention deficit hyperactivity disorder (adhd): a study protocol for a parallel, randomized, double-blinded, single-center trial

Attention-Deficit/Hyperactivity Disorder (ADHD) is a neurodevelopmental disorder characterized by deficits in attention regulation, hyperactivity, impulsivity and emotional self-control. Although psychostimulants are first-line treatments, their adverse effects and limited accessibility highlight the need for alternative therapies. Transcranial Direct Current Stimulation (tDCS) is a non- invasive neuromodulation technique that has shown promising results in improving ADHD-related cognitive functions. Objective: To evaluate the efficacy and safety of bifrontal tDCS in adults with ADHD, used as an alternative or add-on to lisdexamfetamine. Methods: This is a single-center, randomized, double-blind, placebo-controlled clinical trial involving 156 ADHD adults. Participants will be randomly assigned to the following groups: (1) active tDCS/lisdexamfetamine,(2) active tDCS/placebo, (3) sham tDCS/lisdexamfetamine, or (4) sham tDCS/ placebo. The intervention includes 20 sessions of bifrontal tDCS (anode F3, cathode F4) over 4 weeks, combined with lisdexamfetamine or placebo. ADHD symptoms will be assessed pre- and post-intervention using the Brazilian version of the ADHD Rating Scale for Adolescents and Adults (ETDAH-AD). Primary Outcome: Reduction in the severity of ADHD symptoms across five domains (inattention, hyperactivity, impulsivity, emotional aspects, and self- regulation) from baseline to post-treatment. Expected Results: It is hypothesized that active tDCS—especially when add-on therapy—will lead to greater clinical improvements compared to other intervention arms. Trial Registration: The Trial was registered on April 24, 2025 on the Registro Brasileiro de Ensaios Clínicos (Brazilian Clinical Trials Registry - ReBEC under the number RBR-10nbjgb9