I guess the most important thing to remember is that everyone's body chemistry reacts to things differently. My son was diagnosed with ADD (not ADHD) about a year ago and was promptly put on Ritalin. Within a day his teachers and I saw an amazing difference in his ability to sit still and do his work. Before he'd be distracted by every little thing. It's been a year now, and I've seen no side effects to speak of. His appetite went down a bit and he lost about 5-10lbs the first few months, but he was a touch overweight at that point anyway. I'm not really sure, but I think he's got a normal appetite now....you can DEFINATELY tell when he's going through a growth spurt :) Plus, I just realized last week...I guess because he'd been on it for so long now I was getting lax with his meds. Didn't worry if he didn't take it over the weekend. Then I started making sure he took it on the weekend too...I actually didn't have to tell him a half a dozen times to do something before he moved. Now, being almost ten, I STILL had to tell him 2 or 3 times, but...I figure THAT'S normal for the age :)
Oh, and after having just checked, as I said, my son was diagnosed a year ago, and is almost ten now, and he takes one 10mg tablet of Ritalin (methylphenidate HCL) twice a day. One with breakfast around 7:15am, and the other at lunch, around 11:45am. I think these tablets are supposed to take a half an hour to kick in, and last for about 4 hours. He doesn't take a dose after school, because we look at the meds as a way to help him get through school mostly, and if I can't handle him for a few hours after school...mind you, like I said, on the weekends, I don't like having to spend a whole day with him not taking his medication...basically because he doesn't do what I ask him to unless I've said it a half a dozen times (no exageration), and then start to get mad and yell and threaten to get/call/tell his dad.