Whoever wrote the Wikipedia page on Ritalin [1] conflates Amphatamine and methylphenidate. "Amphetamine" appears on 24 times on Ritalin's page, 5 times as "amphetamine and methylphenidate"

[1] https://en.wikipedia.org/wiki/Methylphenidate

Adderall [2] is an amphetamine.

[2] https://en.wikipedia.org/wiki/Adderall

I know they're amphetamines, but surely there's a big difference between that and smoking street meth (which is what I assume your friend switched to from cocaine)

Well, if the ADHD drug in question is Adderall, which is an amphetamine, the mechanism of action and effects are largely similar. And Desoxyne IS meth. Methamphetamine actually metabolizes into amphetamine in the body.

Methamphetamine is an ADHD drug. I take it for my ADHD, with a legal prescription of course.

Ironically it's the most subtle and gentle of all the ADHD stimulants, at least at therapeutic doses. It has a bad reputation because of the abuse of illicitly manufactured meth available on the black market but it's completely unwarranted.