Mary Jane Ward's book, the basis for this film, was an autobiographical account of the author's experiences in psychiatric hospitals. The book caused considerable controversy upon its publication in 1946, as it was a scathing indictment of the treatment of psychiatric patients, a subject considered taboo in the 1940s. Naturally, the book was a runaway bestseller.
The title stems from an ancient practice of dealing with the mentally ill where they were thrown into a pit of snakes. The theory was that something like that would make a normal person insane, therefore it must work in reverse.
Director Anatole Litvak insisted that the cast and crew spend three months visiting mental institutions and attending psychiatric lectures to prepare themselves for the film. Olivia de Havilland willingly threw herself into the research. She attended patient treatments at the institutions, and observed electric shock therapy and hydrotherapy first-hand. When permitted, she sat in on doctor-patient therapy sessions. She also attended social events for patients at the institutions. After seeing the film, a "Daily Variety" columnist questioned whether any mental institution would really allow violent inmates to dance with each other at a social event. De Havilland personally called the columnist to confirm that she had attended several such dances at institutions.
Stephen King has said that watching this film on TV as a child deeply disturbed him and made him feel that he could suddenly go insane, directly contributing to his macabre interests and subsequently his writings.
The character of the gentle psychiatrist was based on the real-life career of Dr. Gerard Chrzanowski, who told his patients to call him simply "Dr. Kik." Dr. Chrzanowski died in November, 2000 at age 87.
Ginger Rogers wrote that she turned down the lead in this film, as well as To Each His Own (1946), both of which Olivia de Havilland accepted. Olivia won an Oscar for "To Each His Own" and was nominated for this film. Rogers wrote: "It seemed Olivia knew a good thing when she saw it. Perhaps Olivia should thank me for such poor judgment".
The portrait on the wall in Dr. Kik's office is of Sigmund Freud. Although his influence has waned somewhat with the rise of neurological and biological research, during the filming of this movie Freud's theories were by far the most prevalent and influential of any psychiatrist, particularly in America. Thus, it was fashionable and quite common for psychiatrists to have either a portrait/picture or sometimes even a bust of Freud in their office.
In his autobiography, writer Arthur Laurents said that he had been hired by director Anatole Litvak to rewrite the first draft of the screenplay by Frank Partos and Millen Brand, which he did. Partos and Brand wanted the WGA to rule that they were the only writers and to delete Laurents' credit, so they submitted the script to an arbitration and presented carbon copies of Laurents' work as their own. The WGA removed Laurents' credit, even though several years later Brand admitted to Laurents that he and Partos had created forged carbons to make Laurents' work look like theirs.