FictionOnlyReader
Why would they study something like essence of insanity? It has no practical purpose... rather a bad choice for a made up potion to add to the story.
Nobody said something about practical purpose for 17-18 years old? Learn to read. But a truth serum and Transformation potion have a use. While something called essence of insanity has only purpose in the dark arts which aren't taught in Hogwarts. Some people should learn to use their Brain more...
MrWeirdo:Then please explain to me the practical purpose of Veritaserum or Polyjuice for 17-18 year olds?