Hmmm! I wonder... think this could be a difference between generic and specific meds? Oh! and, the healing potions are for physical damage, aren't they, whilst those medicines are for illnesses. So the healing potions are basically a tonic, that'll do you some good, but also not do any harm if there's nothing wrong with you and you take it. Where as taking proper medicine that you don't need... oh dear, that can do all kinds of nasty things, can't it!
So I really like that TNT paid this level of attention to detail with regard to this!
I mean they could have made your pet get ill with a disease; by taking a cure for it when they didn't need to, so I'm really glad they didn't decide to go down that route! xD