A herb that works as a slow acting poison when it enters the body. It is known to cause it's victims to bleed from their seven holes(the eyes, ears, nose, and mouth). The poison also greatly weakens them by making it impossible for them to use Soul Force. Traditionally, there was no known cure and a person would be dead within an hour of it entering their system.
Since it has an even stronger effect on the draconic tribe, Ye Han choose to use this poison when he attacked Ye Zong. However, he was unaware that just a few hours earlier he switched his Black Scaled Earth Dragon Demon Spirit for that of the Snow Wind Great Ape with Spiritual Wisdom. This most likely saved his life as the effects of the poison slowed down.
Nie Li later revels that what actually happens with the draconic tongue herb is that it slowly paralyzes the victim giving them the appearance of being dead until their heart finally gives out. He is able to save Ye Zong by using the Daoyin Technique to draw it out of his system.