A drug for tention-deficit hyperactivity (ADHD) alters the structure of children's brains, researchers have discovered when they warn doctors not to prescribe unless it is absolutely necessary.
Scans of children with ADHD taking methylphenidate, best known as Ritalin, showed significant changes in the distribution of white matter, which is important for learning and coordinating communication between brain regions.
The difference between these children and other ADHD patients who received placebo was apparent after only four months.  A similar study in adults showed no changes in white matter between participants of methylphenidate and placebo, suggesting that the brain is vulnerable to structural change in development.
The study's authors warned that the long-term consequences of Ritalin on the brain are unknown, saying the drug should only be given to children who are significantly affected by ADHD.
This amounts to just over 1.5 percent of boys and about 0.35 percent of all girls of these ages.
The study also follows growing concerns in recent years that college students – whose brains are still developing – illegally acquire prescription drugs to improve their concentration.