Meth is only prescribed for ADHD in the US. Is it prescribed for ... nevermind, you edited your post. (Original said something to the effect of "meth is prescribed for drowsiness in pilots," which is inaccurate for the US.)
You'll nearly universally get straight d-amphetamine at the doctor's office.
Vyvanse is d-amphetmine bound to lysine, turning it into a prodrug (which means your gut chemically cleaves off the lysine and, conveniently, you're left with d-amp sitting in your gut).