Poison Items are divided into four categories based on application mode, each one has is description with primary and secondary effects and application mode.

The modes explained:

  • Inhalation: This is the easiest poison, you use a grenade like item with an area of effect, creatures in the area suffer the effect of the poison. The grenade is thrown on area so the projectile effect is not like a “Homing Missile”, the flask impacts where you click.
  • Injury: This is the second easiest way to use a poison, coat a weapon. It is based on the standard system with some little differences. You can coat slashing or piercing weapons, or ammunitions/throwing (bows and crossbows can’t use the itemproperty). Use the item “Poison” on a valid weapon or yourself (the script search for weapon in hand), if the weapon is valid poison will be applied. Don’t use different poisons after coating a weapon or the “charges” will be reset (no stack effect allowed).
  • Contact: It is like Injury but you can coat only bludgeoning weapons or gloves, you can try to perform a melee touch attack, with higher rate to poison yourself.
  • Ingestion: This poison type is used with normal potions or beverages (beer, wine, spirits). The item power must targets one of those items to poison them, when poisoned potions or beverages doesn’t change item description or property. When used the Spell Hook system checks if potion or beverage is poisoned and runs poison script or normal spell script.
  • Extra: With the ingestion system Ombra added a new spell, Detect Poison to recognize infected potions. It is a level 0 spell for clerics, druids, wizards, sorcerers and a level 1 spell for rangers and paladins. The caster makes a Wisdom check with DC 20, if he fails and the caster has Alchemy skill points he can retry with an Alchemy check. If one check is passed the poison is detected (the potion or beverage must be poisoned of course) and the poison’s name revealed. Ombra also modified Neutralize Poison to allow infected potions as a target, if poisoned the spell will now remove the poison from potions or beverages.
  • Spell: Some spells affect the subject with poison or may be used to apply poison on a weapon without risk. The Poison DC of these spells usually scales with casterlevel.

Applying poison on a weapon is a one round action. The poison lasts for 4 rounds or 1 hit whichever comes first. You must make a dexterity check against the DC of the poison to not poison yourself.
There is an exception however: If you have the Use Poison feat: Applying poison is a one round action. The poison lasts for 12 rounds or 3 hits whichever comes first. No dexterity check needed.

Special poisons can be aquired at various locations and from DM events. The Thieves Guild is a rumored to be a supplier in Baldurs Gate and it's environs although the Fists have not yet been able to link them to any assassination attempts.

You can read more about this system Here

The system itself is a customized version of the one Ombra published on the Neverwinter Vault, curtesy of Luna and Rasael.