Poison is a negative effect that lowers attributes.
When a character takes damage from an attack with a poisoned weapon, touches an item smeared with contact poison, consumes poisoned food or drink, or is otherwise poisoned, he must make a Fortitude saving throw. If he fails, he takes the poison’s initial damage (usually ability damage). Even if he succeeds, he typically faces more damage 1 minute later, which he can also avoid with a successful Fortitude saving throw. The Fortitude save DC against a creature’s natural poison attack is equal to 10 + ½ poisoning creature’s racial HD + poisoning creature’s Con modifier (the exact DC is given in the creature’s descriptive text).
One dose of poison smeared on a weapon lasts for 3 rounds, and while the poison is still potent, the wielder of the poisoned weapon may poison as many targets as can be hit in that time. However, since applying the poison is a full round action, it can be difficult to poison 2 or more targets with a single dose.
Although supernatural and spell-like poisons are possible, poisonous effects are almost always extraordinary.
Use of the Heal skill will remove the poison upon a successful DC check of 15. However, it will not remove any ability score damage resulting from the poison's effect. Rest or recuperative spells are needed to repair ability score damage caused by poison.
Special: A Giant spider animal companion will receive Poisonous attacks for free at 1st level allowing them to do Strength damage with their attacks.