1. They are different chemicals.
2. They are administered by different means (inhalation is vastly more impactful than swallowing a tablet).
3. The doses for pharmaceuticals are much lower.
By repeating this argument you create prejudice against those of us who live with ADHD and rely on medication to function normally.
That's rich. Here's a prominent psychiatrist's view (who btw, supports and does prescribe amphetamine adhd medication):
"There's a lot of confusion around the difference between amphetamine and methamphetamine. On the one hand you have anti-psychiatry activists who will say that using Adderall for ADHD is exactly like giving kids crystal meth; on the other you'll have people who say that obviously normal amphetamine is okay, but meth-amphetamine is a demonic substance that will hijack your brain and destroy your life. The truth is more complicated.
Methamphetamine crosses the blood-brain barrier more effectively than unsubstituted amphetamine, but I'm not sure how much that matters since people take different doses of both, and a high dose of unsubstituted will end up with more reaching the brain than a low dose of meth. It seems to inhibit the dopamine transporter more effectively, which might matter, but I'm not enough of a pharmacologist to know how much. Meth takes effect more quickly, which seems to increase addictiveness in a sort of behaviorist sense where the sooner a stimulus gets reinforced, the more rewarding it will feel.
I think there's been a little bit more research since then, but the general takeaway - that the science doesn't support the vast gulf between these two drugs in the popular imagination - still seems true."[0]
[0]https://astralcodexten.substack.com/p/know-your-amphetamines
Note that you are also creating prejudice against an already marginalized group of people, a subset of whom may have undiagnosed ADHD.