Other drugs lose efficacy at different times too, of course. But most still won't do you any harm (except for not helping the issue you're seeking to remedy), which was the OP's point, right? Or am I misunderstanding things.

> except for not helping the issue you're seeking to remedy

... which is harm. If you've applied appropriate medication to deal with the issue, but that medication has gone bad, then you're in a position where you think you've applied a remedy but haven't.

Even if you later find out that the medication was bad, you have no idea how much effectiveness there was left, which affects future dosage calculations.

I have to think they must, considering they need to be refrigerated. (Or at least the ones I've used did)

Some even become toxic, like tetracyclines!