Currently, you only gain exp when crafting items, not when using the resulting items. Or, if the items are used in combat, you might get combat skill exp, such as throwing exp for throwing a fire potion.
If a system was designed to track who created a potion, and when it was used, we could award exp at time of use. So, a player might get 1000 exp for crafting an attack potion, and 5k for killing a monster with it. Alternately, if you kill a monster with a thrown (crafted) attack potion, you might split the exp award between throwing and alchemy.
A similar effect could be devised for buff or healing potions, albeit at a reduced rate of exp gain, to prevent it from being too abusable.
I suppose implementing such a thing might be rather complex.