Shadowcaps are mushrooms found throughout Westeros. They are not typically found in pristine condition while traveling because of how quickly their caps bloom then wilt and crack.
When ingested, Shadowcaps cause a person to hallucinate briefly before passing out. It is imperative that anyone under the influence of Shadowcaps be fed and watered while they are under the effects. There is no time limit to the effects; the affected individual must be brought to a medical facility to be revived. The recovery time is equal to the time left untreated.
Recovery requires a pristine Shadowcap and properly trained medical personnel and tools.
To be kept pristine, a Shadowcap must be placed in a sealed jar at the time of its harvest and be kept in a dark, cool environment.
Pristine Shadowcaps are readily available at alchemist shops for around 10gp each.
There are stories of those who can use divine words along with a pristine Shadowcap to heal those who have been affected. These are only stories; no one has supplied any proof of this power being true.