I'm curious what has led you to believe ADHD is over-diagnosed. I can point to a few papers that indicate ADHD is under-diagnosed in certain population slices, like adult women.

I'm also wondering why you believe doctors are writing scripts for ADHD medications willy-nilly, then sending patients on their merry way. In my experience, the opposite is true:

When someone with ADHD moves across state lines in the US, their new general practitioner doctor typically needs confirmation from an in-state psychiatrist (MD) before they'll write a prescription - even if you've been taking the same medication at the same dosage for years prior. GPs sometimes require that the patient be undergoing therapy too, which is a lot to coordinate on top of a cross-state move. Therapists are also licensed at the state level.

This isn't because GPs are trying to be hard-asses, but because there are strict federal regulations on prescribing ADHD medications in the US.