An imaging study reported changes in gray- and white-matter indices within one to two hours of stimulant medication. The speed of those changes makes it particularly important to distinguish an MRI-derived structural measure from demonstrated tissue growth or repair.
The study included 42 healthy controls and 36 adults with ADHD. Everyone underwent MRI before and after medication. Healthy controls received 30 mg short-acting methylphenidate; the ADHD group received clinician-selected methylphenidate or lisdexamfetamine after a 24-hour medication pause.
This was a human before-and-after study without a placebo arm. Because the pooled sample included different medications and treatment histories, its overall findings cannot be attributed specifically to lisdexamfetamine or its active amphetamine metabolite. All participants also completed the unmedicated scan first.
Pooled analyses identified apparent increases in selected regional gray-matter volumes and more widespread cortical thickness, alongside increases in fractional anisotropy in selected white-matter tracts. Direct group comparisons did not establish significant differences between controls and ADHD participants in the principal structural measures before or after medication.
Heart rate and blood pressure also changed, but correlations did not establish a relationship between those changes and the structural-index changes. A nonsignificant correlation does not rule out every physiological contribution; it limits the particular relationship supported by the measured data.
Voxel-based morphometry, surface-based morphometry and diffusion imaging estimate tissue-related properties from MRI signals and processing methods. A change in those estimates does not directly demonstrate new neurons, repaired myelin or reversal of an underlying disorder.
The authors emphasized uncertainty about the mechanism, lack of placebo control and limited power for between-group comparisons. These findings suggest that medication timing can matter when interpreting longitudinal scans. They do not establish permanent structural change, drug-specific efficacy or an individual impairment threshold. The distinction is especially relevant when comparing a scan obtained after medication with one obtained under different exposure conditions.
Read our analysis of brain-volume changes during methamphetamine treatment and training.
Acute Effects of Stimulant Medication on Gray Matter and White Matter Indices in Healthy Controls and Adults With ADHD. doi:10.1002/brb3.71606.