Rohypnol is a benzodiazepine similar to Valium, Xanax, and Librium. However, its sedative effects are 7 to 10 times stronger than that of Valium. Rohypnol works by depressing the central nervous system. Rohypnol, which played a starring role in the popular movie, "The Hangover," is the brand name for Flunitrazepam, widely known as the amnesia-inducing date rape drug, Roofies. Less known is that this drug is sometimes legally prescribed as a short-term hypnotic to treat insomnia, or for pre-medication in surgical procedures. It is illegal without a prescription in the United States.