This spell is an improved version of slow poison, with a duration measured in days rather than hours. When cast upon a victim who has been poisoned by any means, hold poison arrests the venom and prevents it from doing any additional damage to the victim. (In most cases, the spell must be cast during the poison's onset time in order to be effective.) Damage that has already been inflicted is not restored, but as long as the hold poison is in effect, the victim can be cured or healed of damage caused by poison by any normal means.
This spell can be used to indefinitely postpone the onset of a poison if the caster chooses to continue to cast it on the poisoned character before the previous hold poison wears off. However, each time a new hold poison is used to stop the venom's advance for another few days, there is a 2% cumulative chance that the spell fails and the poison runs Hold Poison its course. Evil priests have been known to deliberately poison a person and then use this spell to grant the victim a stay of death for a few days. This can be an extremely effective threat if the victim doesn't have access to a neutralize poison spell.
The material component is the priest's holy symbol and a bud of garlic, crushed and smeared on the injury (or eaten if the poison was ingested).