> I’ve never been asked to sign a waiver
That presumably has to do with the risk profile of the medications you've taken. If there was a high risk of devastating side effects and it was off label presumably the prescriber wouldn't be willing to take on the liability.
Do you know that for a fact or are you just guessing?
I would wager if those waivers actually did anything they'd boilerplate a generic version of it in the legal mumbo jumbo you have to sign even if you come in to have the doctor look at a stubbed toe.