That's actually a very interesting question. One could theoretically research this by giving amphetamine to people in comas and seeing if they start gaining or losing weight when their diet is unchanged....
Haha I should go get a phd on that. At first, it seems obvious that they'd lose weight, given that metabolism would increase. But then, it seems that with chronic usage, it would level out, and it'd prossibly decrease more than it increased if the dosage wasn't constantly raised with tolerance issues.
But on the other hand, I'd imagine there'd be a dosing interval it allows tolerance effects to recover. I've been taking adderall for the past 10 months without any tolerance increases by taking it 2-3 times a week. I'd have one day on the weekends where I'd fatigue and sleep about 12hrs. So it does seem like I make up for it somewhat.