Let me know if these rules seem good enough.

Replace the injury poison description on DMG257 with the following:
Injury. Injury poison can be applied using an action to weapons, ammunition, trap components, and other objects that deal piercing or slashing damage, which envenoms the item. Injury poisons are either persistent or transient, which determines how they lose their potency. All injury poisons lose their potency when washed off. A creature that takes piercing or slashing damage from an envenomed object is exposed to the effects of one poison. If two or more injury poisons envenom the same weapon, randomly determine which one the creature is exposed to.
Persistent Injury Poison. If a poison specifies a duration when applied to a weapon or other injurious object, and does not specify that it loses potency on a hit, then it is a persistent injury poison. After the duration specified, the weapon is no longer envenomed by the peristent injury poison, as it loses its potency after the specified time.
Transient Injury Poison. When a creature takes damage from a weapon envenomed with a transient injury poison, the poison loses its potency and it no longer envenoms the weapon. For example, if a dagger envenomed with purple worm poison and serpent’s venom is used to strike a creature, the creature is exposed to one of the two poisons determined randomly, then both lose their potency and neither envenoms the weapon.

The poison rules as written are incomplete, and the above text should allow them to function without stacking. As written, the game offers basic poison (which I will rename and offer some other types), which is duration based- it is a "persistent injury poison" in my new lingo above- and it offers four poisons described as "injury poisons" in the DMG. As written, those poisons stack (in stock 5e you can apply drow poison, purple worm poison, serpent venom, and wyvern poison, and a struck target must make four Constitution saving throws at DCs 8/13 (8 to avoid sleep, 13 to avoid poisoned for an hour), 19 (or take 12d6 poison damage), 11 (or take 3d6), and 15 (or take 7d6). The damage saves are half damage on a failure).

A case could even be made that you could apply multiple doses of a poison and have them all effect the target, because it could be argued that the envenomed state is not a game effect. But even ignoring such a claim, this type of poison mechanism isn't what I want.

Further, I want to be able to add poisons without this stacking concern: if you added an "Advanced" poison that was more expensive that Basic poison and offered a DC 12 Con save for 1d6 poison damage, well, that would stack with Basic poison as written.

I believe with the rules above, poisons will work as I feel we all kinda expect them to.

Any thoughts? Did I miss anything?


I first ran into this while making the grass field ninja. I had to add logic to clear the potency of the existing poison and to repeat parts of the injury poison definition (the injury poisons as originally written lasted forever or something, so errata was added), and it was a bit of a pain to make it work right without sounding awful to read.