Mateintwo, that may be the dictionary definition of out-of-date but the expression is also commonly used for medication that has expired. A lot of these listings are from health web sites.Out-of- date (= gone out of style) you use most often referring to fashions but can also be applied to ideas or manners (like kissing a woman’s hand).
With medicines the correct word is: Expiry date. I never read on a bottle of medicine. Do not use this product after the out-of-date date.
Translating that as "If the medicine/medication is out of date it will no longer be effective" is perfectly acceptable."se il medicinale è fuori dalla data di scadenza non sará più efficace"
Of course, Tim! I'm from London, it's true, but I don't say 'eadache, so my pills won't either!
And I'll bet it's even said with "received pronunciation"!