100% of the films screenplay is taken directly from a letter Marilyn Monroe wrote in 1961 about her four days spent in a psychiatric ward of a New York hospital against her will.
The newspaper Monroe reads in the film is fake, but filled with stories typed up by the PD about relevant news stories happening in New York during that week in 1961.
Paige Locke, who plays Monroe, is not wearing a wig. She cut and bleached her hair for the role.
The first thing you see are pink roses. Though not mentioned in the letter, they were really a gift from Joe DiMaggio.
Marilyn writes that she is reading "the letters of Sigmund Freud". The copy of the book you see in her hospital room is an actual copy published before 1961.