If we're talking Adderall/amphetamine salts, I personally don't understand why it's called "addictive." When my insurance has lapsed, and I can't get to a doctor to write the next month's prescription, I have stopped cold turkey to preserve what I have for days I might really need to be on the ball (think job interviews or similar) with no symptoms of any kind of withdrawal (outside of being more lethargic/unmotivated and easily distracted as is my natural state).
I can understand considering it a problem that the effect weakens - requiring more of it to have as strong an effect as when you first took it, but that's NOT the same as an "addiction" as far as I'm concerned - I have no overwhelming need for it, which is probably why people can forget to take them. I do find that being off of it for a while gives the first few times back on it a slightly stronger effect than it had been having when I stopped, although nothing is ever "as good as the first time."