They are different drugs in the sense that methamphetamine will cause more serotonin release and will act longer than amphetamine, but they will both cause increase in blood pressure, increase heart rate and increase internal temperature. The rest of your comment is right though.
They are equally legal in the US (Schedule II). Label will usually say something like "Methamphetamine, generic for Desoxyn." It is, however, much harder to find a doctor that will give you a prescription as compared to other stimulants, and some pharmacies will refuse to fill it.
Believe it or not, marijuana (since 2018 only strains containing significant levels of delta-9 THC) is illegal in the US in almost all circumstances, but methamphetamine is legal with a prescription.
I mean, yeah. Their point is that the substances are extremely chemically similar to the point where they can be treated as different intensities of the same drug.
Yeah that is what I was getting at in my first reply. Amphetamine is a party drug, meth is what junkies on the street use. The guy I responded to said meth, which carries a lot more stigma, and together with all the other negatively charged statements he made is just abhorrent, basically calling her a junkie that deserved to die.