Hollowthistles are spiky red flowers sometimes used to make a vile tea.
If seven cups, or, presumably, more are downed in one sitting, the drinker's insides liquefy.
After Fitz was injured in Neverseen, Physic (or Livvy) had him drink a cup of this tea every morning for a week. At the end of the week, he was healed from a nasty stinger that had impaled him.
Official Description[]
This drink is most commonly described as "vile" and must be taken in moderation, since drinking too much could cause someone's inside to liquefy. It's one of the best methods to purge poison or venom from the system.
Quotes[]
“Steep one hollowthistle into a cup of boiling water and make him down the whole thing in one gulp.”