What if there was more than just the simple loss of heal poisons available. What if a high lvl alchemist could create potions that sap strength, int, dex.
What if...
There was a poison to drain stamina or mana at a rate similar to poisons effect on health
There was a poison that would act like paralyze instantly fixing you in place for a set amount of time.
There was a poison that caused your character to stop every set amount of time stuck in place as if in a fit of pain or illness.
There was a potion that was created with a poison potion like one of the ones above + explosion potion that creates a gaseous cloud
Might make poisoning more useful or even make some monsters more dangerous