Yes, people with ADHD or ADD have a different composition of chemicals in their brain thats why these medications are more effective to them.
Ritalin isn't speed based, but it will keep you going and keep your mind on track. I don't know what happens if you take more than normal dosage with Ritalin, but I know for Adderhal if you take 2-4 pills you will be sky high and feel like supaman