Hypnocil is a fictitious, experimental drug used in the A Nightmare On Elm Street series of movies, specifically in Dream Warriors and Freddy vs. Jason. As explained in the movies, it is used for the suppression of dreams, but has not yet been approved by the Food and Drug Administration (FDA). This is true even after the more than 15 years that take place between the two movies it is featured in. Its mechanism is similar to that of anti-epileptic drugs except that it works during sleep time only preventing the REM phase of sleep. It is useful against Freddy Krueger in that he can only affect (and therefore kill) a person who is asleep and dreaming. When a person is on this drug, he is essentially powerless to hurt them.
In the first script for the third Nightmare on Elm Street film written by Wes Craven and Bruce Wagner, it was spelled "Hypnocyl." In this script it was also supposed to be effective in treating manifestations of psychotic disorders and night terrors.