Monocane is a fictional drug in the 1933 film The Invisible Man. In that film's sequel, The Invisible Man Returns, its name is changed to Duocane.
Described by Dr. Cranley as "terrible," monocane was an obscure Indian drug with powerful bleaching properties. German scientists experimenting with it tried it on a dog, turning the animal dead white and driving it mad. Monocane was used by Dr. Jack Griffin as a key ingredient in his invisibility formula (something he did without knowing about monocane's ghastly side effects). Years later, Griffin's brother Frank's used the drug in his experiments as well.