Quite a while. Think of the strength available of the active ingredient gradually dropping from the date of manufacture till it "degrades to nothing". That le

Quite a while. Think of the strength available of the active ingredient gradually dropping from the date of manufacture till it "degrades to nothing". That length of time is a lot longer than the time period from date of manufacture to the expiry date which is the expected date that the active ingredient degrades to (say) 90%. On that date there will still be that 90% strength of active ingredient. Sure, it won't be the full 100%, but I would willingly take that 90% rather than go without. In the old days, adrenaline injections used to gradually discolour from transparent, colourless (full strength) down through straw-coloured (still pretty good) to orange (not so good) to light-brown (pretty poor) to dark-brown (chuck it away, already). I haven't checked any EpiPen for several decades, so I can't remember whether they change colour or not over time.