Do any legitimate uses for methamphetamine exist?

Yes. Methamphetamine may be used for adhd (attention deficit hyperactivity disorder) and obesity.
Yes. Methamphetamine is almost always a drug of abuse. It is however fda-approved, in the form of methamphetamine hydrochloride) for oral use in treating both add and obesity, under the brand name "desoxyn". It is little used compared to other add meds. It's also used at times by some drs for resistant forms of depression. Used strictly as rx'd, it can be safe & effective. But be careful=>speed kills!