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.
Methylphenidate is a stimulant medication commonly prescribed for ADHD. It works primarily by increasing dopamine and norepinephrine activity in the brain, which can enhance attention, concentration, and impulse control. The drug is also used to treat narcolepsy, a sleep disorder characterized by excessive daytime sleepiness.
Typically taken orally—via tablets, capsules, or liquid solution—methylphenidate is classified as a controlled substance in many countries due to its potential for misuse. It is sometimes misused by individuals without prescriptions in an attempt to boost academic or cognitive performance, a practice that carries health risks and ethical concerns.
Study author Jung-Chi Chang and colleagues sought to investigate whether cumulative exposure to methylphenidate was associated with structural changes in the brain’s frontal lobes, and whether these changes were related to ADHD symptom improvement—especially in relation to the age at which treatment began. The researchers hypothesized that starting methylphenidate treatment during childhood (before age 12) would be more likely to affect brain development than starting during adolescence or adulthood.
The study included 89 individuals diagnosed with ADHD and 91 typically developing controls, matched on age, sex, and intelligence quotient. ADHD is a neurodevelopmental disorder characterized by persistent inattention, hyperactivity, and impulsivity that interferes with daily functioning and development.
Participants with ADHD were recruited from the child psychiatric outpatient clinic at National Taiwan University Hospital, while control participants were recruited from nearby communities. Magnetic resonance imaging (MRI) scans were conducted at baseline and again approximately five years later (ranging from 2.2 to 9.1 years). Parents completed the SNAP-IV questionnaire to assess ADHD-related symptoms at both time points.
The researchers reconstructed each participant’s methylphenidate treatment history using parent reports and electronic medical records. All ADHD participants had used methylphenidate, and none were treated with other stimulant medications such as dexamphetamine, which is not approved for use in Taiwan. The researchers calculated cumulative dosage by multiplying the dose by the number of days taken between assessments.
Among participants who were younger than 12 years old at baseline, those with ADHD showed distinct developmental trajectories in frontal brain regions compared to typically developing controls. In this early-exposure group, higher cumulative methylphenidate doses were significantly associated with increased gray matter volume in multiple frontal regions, including the right paracentral, caudal middle frontal, superior frontal, lateral orbitofrontal, rostral middle frontal, and precentral cortices, as well as the left pars opercularis, paracentral, and superior frontal cortices.
Increases in volume in some of these same areas—such as the right rostral middle frontal, right paracentral, right superior frontal, and left paracentral cortices—were also associated with greater reductions in oppositional symptoms, suggesting a possible link between frontal brain development and behavioral improvement. However, these brain–behavior correlations did not remain statistically significant after correction for multiple comparisons.
In contrast, participants who were 12 or older at baseline did not show significant structural changes in relation to cumulative methylphenidate exposure. However, in this older group, higher cumulative dosage was still associated with greater improvements in inattention and overall ADHD symptoms, indicating that methylphenidate can be clinically effective even when started later, though without the same measurable brain structure associations.
“Our findings indicate that early methylphenidate exposure may affect frontal brain morphology and its association with symptom improvement in ADHD. These age-dependent patterns of psychostimulants on brain structure provide further insight into treatment response and disorder progression monitoring,” the study authors concluded.
The study sheds light on potential effects of methylphenidate on young brain development. However, study authors report that there were many more male than female participants in the study and it remains unclear whether the observed effects are gender dependent. Additionally, drug holidays (periods when participants were not taking drugs) were not systematically documented, and thus not included in cumulative drug dosage calculations.
The paper, “Age-dependent effects of cumulative methylphenidate exposure on brain structure and symptom amelioration in youth with ADHD: A longitudinal MRI study,” was authored by Jung-Chi Chang, Hsiang-Yuan Lin, and Susan Shur-Fen Gau.
