I should have been clearer - I was just trying to be concise to prove a point. And I'm making the assumption that we're comparing drugs of high quality in either category (because obviously drugs that are mixed with adulterants are going to have other problems). You seem to understand what's going on, but for anybody else who's curious:
Adderall isn't methamphetamine. However, the methyl group doesn't change the way that the drug affects the brain; it just makes the drug cross the blood-brain barrier more easily. The increased bioavailability means that less of the drug (by weight) is needed to achieve the same result, but the drug isn't activating any different receptors or having a substantially different neurological effect in any other way or for any other reason. Subjectively, there may appear to be a difference for that reason (more efficient access to the brain), but the same pathways are being accessed - just to a greater degree.
An analogous and more familiar (but not identical) example would be Vyvanse and Adderall. The actual metabolic process is different from the example above, but in essence, about 50% of Vyvanse is lost when converting from a form which has no effect on the brain to a form which does. Once it's converted, it's chemically equivalent to Adderall. That's part of why Adderall XR is prescribed in doses about half the weight of Vyvanse.
[Nitpick: Yes, this isn't a perfect analogy; pharmacology is complicated! Vyvanse contains a single enantiomer of a single amphetamine; Adderall contains two enantiomers each of two amphetamines, but if you know that, you probably already know everything else I'm clarifying here anyway. The reason Vyvanse has reportedly lower side-effects is because it lacks the less effective l-enantiomer, not because the amphetamine is otherwise radically different.]
Maybe I should have been a bit clearer, but my point was that Adderall (legally prescribed amphetamine), Desoxyn (legally prescribed methamphetamine), [street] methamphetamine, and [street] amphetamines ('speed') are pharmacokinetically different because of the way that they are taken, the mode of ingestion, and the set & setting, not because of the active ingredient itself. In general, people don't seem to understand that difference, and for that matter, neither do our laws.
[Disclaimer: Everything I've said above is 'false' in the sense that it is an oversimplification, but this is HN, not a discussion board on pharmacology, so I'm sacrificing some precision in favor of accessibility/simplicity and (attempted) conciseness.]