A longitudinal neuroimaging study of youth with attention-deficit/hyperactivity disorder (ADHD) in Taiwan found that higher cumulative doses of methylphenidate were associated with increased gray matter volume in several frontal regions of the brain. However, this association was observed only in participants who began treatment before the age of 12 and was absent in those who started later. The findings were published in Progress in Neuropsychopharmacology & Biological Psychiatry.