Three items in game share the name Potion, and they each uses the same picture making it hard to tell them apart. Two of the three potions are healing potions one heals 20 HP and the other heals 10 HP. The last Potion is poisonous and damages the user 3 HP. Potion(-3) is the only non-benefital item.
Both Potion(+20) and Potion(+10) cure poison, Potion(-3) does not.
These are the only items in game that can be used by all three classes.