I tried the stuff as a kid and in undergrad -- I was diagnosed with ADHD. It very much helped me concentrate, but stopped me from thinking creatively, clamped down on my ability to think socially, and gave me damned irritating headaches.
Today, I'm more successful with no drugs and an improved work ethic. And less headachey.
Today, I'm more successful with no drugs and an improved work ethic. And less headachey.