Adderall is a mixed salt, it's two stereoisomers, amphetamine and dextroamphetamine. One of them (I think it's the amphetamine) is "speedier" feeling and the other one (I think dex) is "cleaner".
Dextroamphetamine is also available as a purified salt itself, as dexedrine. And I think that's more of a "kids medicine" specifically because it's less "speedy".
I think there's nothing that guarantees any particular ratio comes in the product, and obviously generics have very mixed results on just how "bioequivalent" it really ends up being. I think the mixture is varying and people end up feeling like it's different because they're feeling the "speediness" change and that's the feeling they associate with being medicated with stimulants.
Amphetamines are another dopamine-releasing and gaba-ergenic family of drugs and my suspicion is that in the presence of an opioid antagonist like naltrexone probably patients would not be able to distinguish between the exact mixtures of the stereoisomers but without it they probably can tell which feels "speedier" and the perception is that is how much their symptoms being treated. The dopamine-releasing loop probably is a not-insignificant part of how it treats ADHD though, dopamine-seeking is a key aspect of ADHD (do you drink caffeine or eat sugar before you go to bed, or when you wake up in the middle of the night, and then fall right asleep? that's because your brain is getting dopamine satiation finally).
(Incidentally this all makes stims a very difficult combination for alcoholics and other GABA-loop drugs because the effects are synergistic and mask each other.)
Obviously a difference in coatings should make zero difference but half the time there are broader problems with bioavailability or just generics being inferior quality in general, not just adderall but in general. The FDA isn't doing a good job with this really, just IMO, and not just with adderall. The entire foundation of generics rests on "this is chemically equivalent and absorbed the same" and it's clearly not for a lot of people and the generic is almost always the one that comes off worse. The entire product needs to be the same, binder and coating and all, with the same level of quality and in the case of stereochemistry it needs to be the same mixture.
The bigger problem is just the shortages in general... my last 2 refills have both taken 7 days past the end of of the prescription, and this latest one I only managed to get 1/3 of my prescription filled (and they won't fill the rest of the prescription later if you pick it up, nor will they hold what they have while the rest of it comes in). Leftovers and reducing my dose (against the instructions of my doctor) will only carry you so far, I can't run 50% longer on a given prescription. The mood swings and stress and dopamine-balance/seeking problems that come with bouncing off it are rough too.
My doctor's office is entirely unsympathetic and views their job as 24-48 hour turnarounds which is obviously completely insufficient for this kind of situation, no way it will be on the shelf in 48 hours. And if I push it then I come off drug-seeking (yes, voluntarily taking 1/3 of my prescription per month so I can get something at all, definitely drug-seeking). It sucks and I've become very disillusioned with my doctor over this, they just are not sympathetic at all.
Everything to do with C2s is just so tainted by the adversarial relationship between the DEA and doctors and that only emphasizes the sometimes-adversarial relationship between doctor and patient.
If this were lupus patients struggling to get their meds during the height of COVID mania, there would be no concern whatsoever about doing what was needed to get people their meds. There would be no concern about other generic providers just making more, either. But it being a C2 changes everything. It fucking sucks and it's disgusting this is how a health care system works.