The differences between Ken Kesey's novel One Flew Over the Cuckoo's Nest and it's movie adaptation by Milos Korman is best described through the strong differences of characterisation. Moreover, the novel and movie are antithetic especially in terms of the Kesey's allegorical message in the novel which is only present latently in director Milos Forman's movie adaptation. Ultimately, movie and novel are two very unlike forms of media and Forman's adaptation is appropriately sways the novel's main purpose.
Kesey's novel is told from the mute Chief Bromden's point of view, whereas the character's role is significantly less important in Korman's movie. Chief Bromden's well-informative backstory is completely removed from the movie. However, his backstory obviously would be almost impossible to show Bromden's pre-hospital life, nor have the movie told from the Chief's point of view as the chief habitually feigns muteness.
Other characters such as Nurse Ratched and Randall McMurphy are slightly altered by the director and screenwriters to better fit the movie. Nurse Ratched is no longer the omnipotent dictator of her ward but is still an intimidating power-player in the ward. McMurphy goes through many states of mind in the novel. At first, Randall McMurphy is calm and collective. Then he is rebellious and docile again after being unjustifiably and maliciously forced into treatments of electroshock therapy. In the movie he is rude and boisterous suggesting the reader to think he is indeed an insane man.
The minor changes to the characters in the movie and novel subsequently change the mood and theme of the media works. Viewers and readers thus interpret the story in different ways. These changes arguably make one or the other of more quality yet one thing is clear, if the original novel is read correctly it gives the stronger and authentic message intended.