Well for that fact of the matter, any potion in a Nordic ruin or any ruin or anywhere really really old.
Now this topic has probably been discussed obsessively by now or so I would believe.
But considering that potions are made from all natural ingredients, wouldn't you say at some point they would expire? Or have expiration dates? I have this uncanny feeling that every time the Dragonborn takes a swig of expired potion, he's having uncomfortable bowel movements.
So, the question to me then is:
Should potions in old dusty ancient ruins, without the presence of bandits, have negative side effects too?
I know it also safe to assume that all the potions are from the bandits or the forsworn. But the best example I have is the very first Nordic ruin you come into. The recent bandits, and that bandit chieftan didn't make it very deep before dying. And I doubt Arvel the Swift left that many potions just lying around.