Since Grimtooth is permanently poisoned, dipping it in an uncursed potion of water should turn it into a potion of sickness, and dipping it into a pool or moat should turn it into sewage.

Brood wasp infection shouldn’t be curable with a unicorn horn. There should, however, be some way to kill off the infection by harming yourself, like drinking a potion of sickness or otherwise poisoning yourself.

Occasionally, when generating a level 6+ spellbook, set its opoisoned flag to true. You get “The book was coated in contact poison!” not as a random spellbook reading failure effect, but when you try to read a book whose opoisoned is set to true. Triggering the contact poison usually (but not always) clears the opoisoned flag, so it won’t be poisoned if you try to read it again.

Dipping a poisoned spellbook in any healing potion will neutralize the poison and use up the potion. Possibly, dipping it in a potion of sickness will poison the book, though this would be useless unless monsters read spellbooks.

Potions of sickness induce vomiting, which can be used in a pinch to cure food poisoning or overeating.

Thrown potions of sickness create a stinking cloud centered on the spot they break. If the potion were diluted, the cloud is either smaller or disperses faster.

Sickness resistance negates the effects of potions of sickness. However, a cursed potion of sickness will now give you fatal illness instead of the normal poison effects.