Edgar Kerval is one of my favorite authors. His books are written from long-time experience, which is a rare quality among contemporary writers, and he has a strong background in many areas of Left Hand Path magic that have not been explored by other practitioners. His "Herbarium Diabolicum" is a pivotal work as well, because it is the first book that not only introduces the reader to the use of mind-altering substances but also provides rituals and other forms of practical application in regard to the Qliphoth and the Path of the Nightside. I have not personally seen a better overview of this subject and I recommend it to everyone who is seriously interested in the poison path.