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.
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.
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.
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.