Milk Drink restores up to 50% of the user's current HP.
If powered up by a Normalium Z into Z-Milk Drink, all of the user's lowered stats are reset.
Outside of battle
Prior to Generation VII, Milk Drink can be used outside of battle to take away 20% of the user's HP and restore another party Pokémon's HP by the same number of points. Milk Drink cannot be used outside of battle if the user's HP is less than 20% of its maximum HP.