Because Amy Adams had just become a mother when shooting began and she's playing a drug addict on the movie, she decided to not use much make-up and incorporate her natural tiredness due to having a baby to the role.
Kristen Stewart agreed to a salary less than $200,000 after the film's budget was drastically cut. Stewart remained committed to the role of Marylou out of her love for the original novel by Jack Kerouac.
Beat scholar Brian Hassett pointed out some of the multiple sources beyond the novel also used/referenced/seen in the movie: Director Walter Salles and screenwriter Jose Rivera used the scroll version of On The Road (published 2007), not the 1957 edition, as the working blueprint. And then all sorts of little touches were added from Neal, Jack & Allen's letters, Carolyn Cassady's autobiography, the 2 different LuAnne Henderson interviews, "The Town And The City," Jack's audio recordings and articles and notebooks, Allen Ginsberg's "Denver Doldrums," "Dakar Doldrums" and the "Martyrdom and Artifice" journals, John Clellon Holmes' "Go," Gifford & Lee's oral biography "Jack's Book" - all noticed specifically.
Before filming began, director Walter Salles had the cast do a three week 'beatnik boot camp'. Kristen Stewart described it as three weeks of nothing but literature about the beatnik generation and listening to audio interviews from Jack Kerouac.
In the book, Dean Moriarty is described as a nervous bundle of energy, an incessant talker whose rapid-fire, stream-of-consciousness patter makes him an endearing character and forges his bond with Sal. His trademark "Yes, yes" is used as an interjection to punctuate his nonstop monologues. In the film all sense of this is lost as Dean has fairly little to say, and his "Yes, yes," frequently spoken but mostly standing on its own, gives the opposite impression that he's not very good with words.
It took roughly five years between Walter Salles agreeing to make the film and actually getting round to filming it, mainly down to financing that fell through. Garrett Hedlund was attached from the start and stayed committed throughout all the fiscal ups and downs. In the intervening five years, every time he was about to commit to a film, he would make sure it was OK with Salles first.
Sal Paradise is presented as the typical Hollywood stereotype of a writer: a thin, wan, introverted spectator of life; a wallflower who sits in the corner writing about the adventures of others, and is drawn into them reluctantly himself. But Jack Kerouac was a star athlete with an imposing physical presence who went to Columbia University on a football scholarship (after turning down offers from Boston College and Notre Dame). In the book, Kerouac's avatar Sal Paradise begins as a neophyte to the "beat" lifestyle but embraces it wholeheartedly and jumps in with both feet. In fact, the idea of experiencing life in every way imaginable rather than watching from the sidelines is his intent from the beginning and the whole point of the book.
Jack Kerouac was very devoted to his mother, and lived with her - or she with him - on and off throughout his life. The film depicts this fairly accurately. But in the book, the character representing his mother was identified as Sal's "aunt". She mostly served the purpose of someone Sal could call and ask to send money as he often found himself flat broke while on the road. Later novels explored their mother-son relationship in detail.
Bull Lee's home in Algiers, Louisiana appears to be a country estate on a large, heavily wooded property with no apparent nearby neighbors. But Algiers is an old, densely populated neighborhood of New Orleans, just across the river from the French Quarter. It is impossible to imagine William S. Burroughs, the inspiration for Bull Lee, living in a rural environment.