You've not made it clear how the potions fit in with your game, is it 2d or 3d? Do you have multiple potions with different functionality and number of uses or just the one?
Assuming 2d and 1 potion, just don't display the potion image if potion = 0
Assuming 2d and 1 potion, just don't display the potion image if potion = 0
Potion = 3 ;...In main loop If mousehit(1) and Potion > 0 Health = Health + 5 Potion = Potion - 1 endif