A high dose of stims makes me as an ADD retard (I call myself that, so chill out) more functioning And, well, stimulated.
It's not like we have a built in resistance to getting high off of the amphetamine class of drugs.
That said, as I've been getting older than I was when I was using/abusing speed daily (the correct use of speed that is. amphetamine powder) I've noticed less and less euphoric qualities whenever I shoot up but there are too many variables in my life for me to say "yup, that is the add's fault".
I don't really understand what you mean by "if it would just increase the medicinal effects"?
Afaik I get the same effect as my friends, but maybe with a little less motivation to do things some of the times I use stims that are probably connected to my depleted dopamine, and a higher dose just makes me talkative, focused while being totally unfocused and doing hundred times at once (atleast at 0.5+doses of speed).
Aaaand i lost track of what I was gonna write to try and answer your question. I'll be back after my Elvanse has kicked in lol