I copied from the link that Rex provided.
Finally, one must also know how to cure poison. Generally, the Cure spell is sufficient to cure Greater Poison and below, although I myself am almost a Grandmaster Mage, so that tends to help a bit.

The most powerful potion is difficult to Cure even with this high of a Magery skill; in my personal experience, I've had to cast Cure three to four times before eliminating a Deadly Poison in someone's system. This spell seems to be somewhere between Deadly and Greater Poison in terms of effectiveness.
Cure potions seem to be the better alternative, since there is no chance of disruption, such as there is when casting spells. Also, a Greater Cure will cure even Deadly Poison with only one quaff. A regular orange potion that was found as loot on an Earth Elemental was able to cure the 5th level Poison inflicted by a Poison Elemental, but that result can not be guaranteed.
To Cure Poison Chart
Potion -
Lesser Cure -
Cure -
Greater Cure
Lesser Poison - Usually* - Always - Always
Poison - Sometimes* - Usually* - Always
Greater Poison - Sometimes* - Usually* - Always
Deadly Poison - Never* - Sometimes* - Always
5th level Poison- Unknown - Unknown - Unknown
* Several attempts may be needed to succeed
A Healer with a Healing and Anatomy skill of both greater than 60 can cure all levels of poisons with a simple bandage. Of course the higher level poisons require a high level of Healing and Anatomy to be successful.
To sum it all up, some good advice for the budding assassin would be to not bother trying to kill people with poisoned food--leave that type of poisoning for skill-gain. On the other hand, poisoning blades will give you a tremendous advantage in both monster and PvP combat (but, again, only if you can manage to get a successful poisoning hit off). Overall, an experienced assassin or poisonous creature is a very deadly foe indeed; adventurers are advised to keep a a few Greater Cures on their person at all times.
Thanks Rex,
Trent