I have extreme ADHD and took Ritalin from the time I was 7-13. Haven't ever took it since then, but I've noticed ever since I started tokin' - that it does help my ADHD, and in more ways then calming my hyperness.
My brain just slows down to a logical speed where I can rationalize on 1 thought at a time, which I can't do sober.
My highs usually last a long time, 3-5 hours.