In old-school games, there was generally one kind of poison. Save or die. That’s pretty final. And kind of boring. Why shouldn’t poisons be as interesting and versatile as potions, spells, or magic items?
Now, I’ve seen some more advanced systems for poisons somewhere. I can’t remember where. There’s just too much gaming junk bouncing around inside my head. So why not just start working on my own. The way I look it there’s four major factors for poisons: Delivery Method, Effect, Time to effect, and Potency.
Delivery Method: Attacks (weapons, traps, and bites), Contact (Just touching the stuff. Traps again), Inhaled, and Ingested. To add more customization, a poison could used with all or some of the delivery methods.
Effect: Here’s the big wide world of poison. Of course, there’s save or die, extra damage, paralyzation, blindness, penalties, ability score “damage”. Let the imagination go wild.
Time to Effect: So how long does it take for the poison to work? Instant, round, minutes, hours, or maybe even days?
Potency: How strong is the stuff? Get a saving throw or not? Any bonuses or penalties to the saving throw? If a character does make the save, is there any secondary effects?
So yes. Here’s the kernel of an idea. Got to work our some simple random tables for this.

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