Various poison vials were introduced in the Hordes of the Underdark expansion. Player characters may use these items on slashing or piercing weapons (or bullets) in an attempt to coat the weapon with the toxin, resulting in a temporary on-hit poison property. (The duration can vary by the type of vial, but all types defined by BioWare have a duration of three rounds.) As coating bows and the like is rather ineffective, their ammunition would be coated instead.
Applying poison requires a dexterity check to succeed:
The apply DC for the standard poison vial types is two more than their save DC. A failed roll is supposed to poison the applier, but this has not been implemented. (Probably a bug.) Assassins and blackguards are trained in the use of poison and may coat their weapons with poison without risk of poisoning themselves. (No die roll is made; the poison is automatically applied.)
On-hit poison properties inflict a poison that deals 1d2 ability damage to a given ability for both primary and secondary damage. The types of poison vials defined by BioWare cover all six abilities, with save DCs ranging from 14 to 26. From these forty-two types of vials, eighteen were implemented as standard items (under "Crafting/Tradeskill Material" in the miscellaneous category of the item palette). The implemented vials are centipede venom (reduces dexterity), giant bee venom (reduces constitution), and spider venom (reduces strength), with their potencies described as weak (DC 16), mild (DC 18), average (DC 20), strong (DC 22), very strong (DC 24), and deadly (DC 26).