It absolutely has, going by people's subjective ratings, different effects on NT people. That's not to say it doesn't work, there are plenty of explanations. We don't really get how neurotransmitters interact, so it's possible these drugs trip some cascade effect which incidentally treats ADD. More likely, there's a good place to be on the tradeoff curve and different symptoms below and above it. Perhaps large enough doses could push through (though I doubt that amphetamines are so well targeted to permit it), but it's fair to say that if I'm at a 0 and Adderall takes me to a 2, and an NT person is a 3 with Adderall taking them to 4, I can get to 2 and they can't. Is that "working differently"? Depends on how you look at it.