So, I am not an administrator and my opinion isn't that of the general administration policy or to be taken as an official stance on the matter but I wanted to weigh in nevertheless.
Popping milk mid combat to prevent you from going down isn't script abuse. You are directly improving your health score during combat with a non-realistic manner to prevent you from losing an RP situation. This is by definition power-gaming. This line however is blurred with stronger substances such as cocaine gum and such like that.
Is it script abuse? No.
Is it powergaming? Yes.
Medicines are stronger substances. "Pre-potting" was a common thing to do especially during war. (Looking at you Jerrys and your methamphetamine). I'd be more inclined to allow this behaviour over eating some game or drinking water before going into combat. It feels like a medium-RP SA:MP behaviour type thing.
Why does Game even improve health then? Well, I think it's fine outside of planned combat.
Medicines giving temporary stat boosts I think is a more than reasonable thing for both IC use, PvP and RP use. I also think paired with an addiction / drawback system it could be quite a tasty little script.