Potions of poison were a type of poison that mimicked beneficial potions, commonly Potions of Healing. They were imbued with illusion magic that made them indistinguishable from other potions by smell, taste, and appearance, and were regularly employed by assassins towards nobility. The illusion could only be revealed by divinatory spells, or broken by abjuration magic.
Drinking a potion of poison immediately poisoned the imbiber, and was toxic enough to kill a regular person within seconds. The poison continued to act after ingestion, until the drinker managed to resist the effects or was killed by the toxin.