"Gene Tierney was the first choice to play Virginia Stuart Cunningham, but was replaced by Olivia de Havilland when Tierney became pregnant.

Director Anatole Litvak insisted upon three months of grueling research. He demanded that the entire cast and crew accompany him to various mental institutions and to lectures by leading psychiatrists. He didn't have to convince Olivia de Havilland. She threw herself into the research with an intensity that surprised even those who knew her best. She watched carefully each of the procedures then in vogue, including hydrotherapy and electric shock treatments. When permitted, she sat in on long individual therapy sessions. She attended social functions, including dinners and dances with the patients. In fact, when, after the film's release, columnist Florabel Muir questioned in print whether any mental institution actually "allowed contact dances among violent inmates," she was surprised by a telephone call from de Havilland, who assured her she had attended several such dances herself.[5] Much of the film was filmed in the Camarillo State Mental Hospital in California." (Wikipedia)

nach dem gleichnamigen autobiografischen Roman von Mary Jane Ward über ihre Erfahrungen in der Psychiatrie (1946)

Set in a mental institution, "The Snake Pit," based on Mary Jane Ward's fictionalized memoirs, is one of Hollywood's first films to deal in a serious way with mental breakdown and the painstakingly slow recovery process. Produced by Darryl F. Zanuck at Fox, Anatole Litvak's film is uneven, containing many intelligent sequences but also some that are just lurid and sensationalistic.

Olivia De Havilland plays Virginia Stuart Cunningham, who is placed in an asylum by her loving husband Robert (Mark Stevens), after realizing that she needs professional help.

The kind, thoughtful and caring Dr. Mark Kirk (Leo Gann) takes a special interest in her case, and Virginia becomes his favored patient. Needless to say, the place is overcrowded with patients and understaffed, but somehow Dr. Kirk spends most of his time with her. He wants to prove that mental institutions are not "snake pits," as the public stereotype goes.

The movie has lost some of its 1940s shock value. Committed to reformist goals, the filmmakers hoped that their film would help improve the conditions at mental health institutions. Watching the film from today's perspective allows us to see its long-enduring impact on other Hollywood films about madness, including "One Flew Over the Cuckoo's Nest."

The central love story is not particularly compelling, but it's surrounded by interesting footage about life in an asylum, done in a semi-documentary style that draws on Litvak's previous experience.

The film was nominated for six Academy Awards, including Best Picture, winning one for best sound recording. Olivia de Havilland was nominated for an Oscar for her stark, gritty performance, but lost out to Jane Wyman's deaf-mute girl in "Johnny Belinda."

Initially, Litvak choice of the leas was Ingrid Bergman, but the actress, then at the height of her popularity declined, based on her feeling that "it all takes place in an insane asylum and I couldn't bear that." Instead, the role went to Olivia de Havilland, who scored a great victory, winning an Oscar nomination and a citation from the New York Film Critics. After the film's success, Litvak confronted Bergman, "Look what you turned down!" "It was a very good part," Bergman replied, "but if I had played it, I wouldn't have got an Oscar for it."

Litvak conducted pre-production research to lend authenticity to his picture that, despite its grim subject, was both a critical and commercial success. "The Snake Pit" also became an "event" movie with real impact. It is credited by some historians for calling attention to mental problems and to changes of practice and legislation in as many as 26 states
http://emanuellevy.com/review/snake-pit-the-1948-3/