ADHD is increasingly recognised as a cause of functional impairment in adults. Treatment guidelines recommend stimulants as the first-line treatment for adult ADHD, but concerns exist about long-term efficacy and potential tolerance. We investigated the long-term effect of stimulant therapy on brain morphometry in individuals with ADHD.

We obtained structural MRI data from the UCLA Consortium for Neuropsychiatric Phenomics for 26 adults with ADHD. We compared grey matter volume, cortical thickness, sulcal depth, gyrification index, and fractal dimension between individuals with ADHD who had received psychostimulant treatment and medication naïve. For clinical assessment, we also compared Barratt's impulsivity score, Dickman impulsivity inventory II, and Eysenck's impulsivity inventory and investigated how brain morphometry were associated with these scores

The treated group exhibited significantly higher values in surface-based metrics (FWE-corrected p-value < 0.05), including gyrification index, sulcal depth, and fractal dimension. There was an increased gyrification observed in the right Rolandic operculum, left supplementary motor area, left superior temporal gyrus, right fusiform gyrus, and left cuneus. Increased sulcal depth was detected in the inferior and superior orbitofrontal regions, while increased fractal dimension was also evident in the left superior orbitofrontal gyrus. Treated group venturesomeness scores positively correlated with the grey matter volume of the right anterior cingulate gyrus and negatively with the right superior occipital gyrus.

Our results suggest a limited treatment effect on ADHD scores and grey matter volume in adults. Despite significant surface-based metrics, these changes were not accompanied by improvements in the clinical scores.