An imaging study has suggested that ADHD medications may work differently than previously thought.Instead of directly affecting attention, they affect arousal and reward networks in the brain.1 A five-year study by Taiwanese researchers followed 89 young people with ADHD and 91 healthy control participants.[The results showed that methylphenidate - the most commonly prescribed medication for ADHD - affected the growth of the cerebral cortex only in children who began treatment before the age of 12.1 Older participants did not show similar changes.[Methylphenidate acts as a stimulant drug that increases dopamine and noradrenephrine activity in the brain, improving attention, concentration, and impulse control.1 The effects of these medications are usually seen in as little as 30 to 60 minutes.[1] Methylphenidate is a stimulant drug that increases dopamine and noradrenephrine activity in the brain, improving attention, concentration, and impulse control.