A werewolf is an animal from folklore which can change from human to wolf and back again and is believed to consume human flesh or blood. (Wer is an Old English term for man.) While there are no documented cases of any human turning into a wolf and back, there are documented cases of humans who believed they were werewolves. To suffer from such a delusion is known as lycanthropy.
Lycanthropy is a psychosis in which the patient has delusions of being a wild animal (usually a wolf). Delusions of being a wolf or some other feared animal are universal and, although rare in the industrialized countries, still occur in China, India, Africa, and Central and South America. Not infrequently, bizarre and chaotic sexuality is expressed in a primitive way through the lycanthropic symptom complex. Patients whose internal fears exceed their coping mechanisms may externalize them via projection and constitute a serious threat to others. Throughout the ages, such individuals have been feared because of their tendencies to commit bestial acts and were themselves hunted and killed by the populace. Many of these people were paranoid schizophrenics.