Early in the film it feels like Anatole Litvak was attempting a gritty realistic exposé of the incapacity of American healthcare, in the style of those docu-dramas that became popular in the US after WWII. Ultimately, The Snake Pit wanders off into melodrama, and its portrayal of a psychiatric hospital failing due to lack of funds and facilities becomes secondary to it's lead character's psychosis which is as much of a McGuffin as Gregory Peck's in Hitchcock's Spellbound.
Still, as melodrama, it is very effective. Virginia Cunningham (Olivia de Havilland) is a middle class woman with schizophrenia who becomes snagged in the net of American public health, which is portrayed as extraordinarily incompetent. Her only hope of getting better rests with Dr. Kik, a handsome pipe smoking psychiatrist (Leo Genn).
In the opening scenes, there is a great deal of soap box editorialising, but the story eventually becomes so conventional that by the end, all the residents are singing Goin' Home together led by a Broadway standard vocal from one of the patients. Olivia de Havilland is deglamourised, but it's still quite a photogenic breakdown.
The Snake Pit is an extremely sensitive and well-meaning film, and there is plenty of artistry, particularly in suggesting Virginia's hallucinatory break down. De Havilland gives one of her great performances of the postwar era when she was perhaps the best female dramatic actor in Hollywood. The Snake Pit tries to be naturalistic and unromantic but this was made in the studio system and that proved impossible at this time.