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Home-based transcranial direct current stimulation (tDCS) improved attention in adults with attention deficit-hyperactivity disorder (ADHD) who were not taking stimulant medications, a randomized trial showed.

Among 64 adults, the mean inattention score measured by the clinician-administered version of the Adult ADHD Self-report Scale (CASRS-I) was 18.88 in those who received 4 weeks of daily treatment with the home-based tDCS device compared with 23.63 in those who received sham treatment, reported Luis Augusto Rohde, MD, PhD, of Universidade Federal do Rio Grande do Sul, in Porto Alegre, Brazil, and colleagues.

Linear mixed-effects models showed a statistically significant treatment by time interaction for CASRS-I (β interaction -3.18, 95% CI -4.60 to -1.75, P<0.001), they noted in .

"Our findings support the use of tDCS as a safe and effective treatment for adults with ADHD with no concomitant treatment with stimulants," the group wrote. "Investigating effective nonpharmacological treatments for ADHD is a pressing concern," given the low rates of long-term adherence and persistence with stimulant medication, the recommended first-line treatment for most ADHD patients.

tDCS sessions shorter than 40 minutes using less than 4 mA have not been linked with any serious or irreversible side effects. Skin redness, scalp burn, tingling, and headache are the most common adverse effects.

The recent availability of reliable home-based tDCS devices has reduced the need for daily office visits and the associated potential for reduced adherence, Rohde and team noted. The dropout rate for this study was 14%, mainly due to COVID-19 restrictions.

Another noninvasive approach to neuromodulation, trigeminal nerve stimulation (TNS), was the first device-based therapy approved by the FDA for children with ADHD.

So far, most studies of tDCS in ADHD have looked at the of targeting the dorsolateral prefrontal cortex (DLPFC), and results have varied, the authors said, citing a that showed some "small trendwise significant effects for inhibition and processing speed, but not attention functions"; pilot studies in and showing that tDCS had an effect on inattention but not hyperactivity-impulsivity; and a large that showed no symptom improvement after 15 sessions of tDCS over the right inferior frontal cortex. However, these studies varied in design, and many had "small sample sizes and short treatment periods," they added.

Like these studies, the current study found "no statistically significant differences in secondary outcomes of hyperactivity-impulsivity, depression, or anxiety," Rohde and team wrote. This may reflect exclusion of people with pre-existing depression or anxiety, or involvement of different areas of the brain in ADHD patients presenting with inattention versus hyperactivity-impulsivity, which has been linked with " in the right inferior frontal cortex rather than right DLPFC."

In the absence of a consensus regarding the optimal montage for ADHD, the group used the right rather than left DLPFC based on reports of decreased activation in this region "in adult patients with ADHD during tasks that require attention," the group noted.

"In a conservative appraisal of our findings, the lowest limit of the 95% CI of the estimated effect size indicates at least a moderate effect, similar to the one reported with TNS, as well as to the second-line treatment for ADHD, atomoxetine, highlighting the potential use of neuromodulation as an effective alternative treatment for this population," Rohde and team wrote.

For this double-blind, parallel study, which was conducted from July 2019 to July 2021 at a single center, the authors enrolled 64 adults with ADHD and moderate or severe symptoms of inattention; 48% of participants had inattentive subtype and 52% had combined subtype. Mean age was 38 years, and 47% were women.

Study limitations included that patients' electrode placement and exposure were not supervised, in contrast to other studies of tDCS, as well as the use of a relatively homogeneous population of ADHD patients with no significant comorbid depression or anxiety. In addition, patients receiving pharmacological treatment for ADHD were excluded, which may limit generalizability.

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