A dream suppressant pill used in Nightmare On Elm Street 3 and Freddy VS Jason. Prevents people from dreaming and keeps them from being attacked by Freddy Krueger, for unless you're dreaming, he can't hurt or kill you. When on this drug, he is essentially powerless to harm you. Kinda like Freddy's version of Kryptonite, an "Anti-Krueger" drug, if you will. This has not been approved of by the FDA, mind you, and will forever be a fictitious drug. Side effects include nervousness and prolonged comas if taken in heavier than reccommended doses.
Freddy Krueger was unable to kill any children at all b/c they were all doped up on Hypnocil. Their parents thanked the lord for it.