You don't become addicted to therapeutic doses of amphetamines. There is some degree of physical dependency, but it's safe to stop taking them cold turkey and would only take ~a week-a month to return to "baseline" after that.

This is actually not true of the non-stimulant ADHD drugs like Intuniv; you have to taper that one off over a few weeks or unpleasant things happen to your heart rate.

And, of course, ADHD patients constantly forget to take their drugs, and the system where you have to get a new prescription every month isn't even something they can reliably do, being ADHD patients.