Potion levels

[Xoris]

I can't remember, or find, what's the difference in the different level potions?

What's the difference between Distillate of Immunization IV and Distillate of Immunization VII, for example?

[Posatrocible]

The levels of the various potions have various differences:

-it might effect spell duration or strength (as with Skinspikes)
-it might effect the potency (as with your Immunization example... the higher the level, the more disease counters removed)
-it usually restricts what level character can use it
-it also might have an effect on re-cast delay

A common question about potion level that I hear in the bazaar is: "What's the difference between philter of the wolf I and V?" This is a clear discussion on this topic.