The Black Sleep (alternate title Dr. Cadman’s Secret) a 1956 American independent horror film directed by Reginald LeBorg, and written by John C. Higgins from a story by Gerald Drayson Adams.

The film was produced by Aubrey Schenck and Howard W. Koch, as part of a four-picture finance-for-distribution arrangement with United Artists.

Cadman gives Ramsay a potion that he calls "The Black Sleep," which induces a deathlike state that can lead to actual death if an antidote is not administered in time.

The next morning, Ramsay is discovered in his cell, apparently dead, and Cadman takes the body, supposedly for burial, with his assistant Odo.

However, when he next meets with Ramsay, Cadman tells him that he is conducting experiments on human brains to help restore creatures like Mungo and his mute servant Casimir to normal condition.

Back in London, Odo has slipped the Black Sleep potion to a woman who knows the truth about the man Curry whom Ramsay was alleged to have killed.

Producer Howard W. Koch described the film's genesis as typical of his arrangement with United Artists, with script, cast, and other elements being driven by the budget given by the company.

This was just ahead of the TV syndication, through Screen Gems, of two decades of Universal monster movies, under the package title Shock Theater.

Writer Higgins, director LeBorg, and stars Rathbone, Chaney, Carradine, and Lugosi had all been significantly associated with Universal horror films or related B movies.

On its double bill with The Creeping Unknown, The Black Sleep was financially successful, with the two films earning $1,200,000 more than their total cost.

[3] Amongst contemporary reviews, Variety wrote that the film "plays the horror tale fairly straight so what's happening is not too illogical until the finale wrapup, when all restraint comes off and the melodramatics run amok.