I have ADD but prescription meds have never worked very well for me. Coffee does. My productivity with caffeine is probably at least 30-40% greater than my productivity without it. For rushed projects or all-nighters I'll uses an energy drink or two instead of coffee or espresso.

The tolerance is an issue but since I'm a student I can use vacations to stop intake for a week and then go back to my usual consumption rate. The existence of safe and legal uppers is probably my only salvation.