Trivia

According to writer and director Paul Thomas Anderson, Joaquin Phoenix and Reese Witherspoon "have their own language and short hand" with each other. While their natural rapport helped to show the chemistry between their characters, this led to Anderson having to constantly remind them to stop chatting so that they could film.

The character Sortilège appears as a supporting character in the novel, and although she does give helpful advice to Doc, she is not the narrator. While writing the screenplay, Paul Thomas Anderson decided the film "needed a female voice" and tailored it specifically for his friend Joanna Newsom. The character also fulfilled Anderson's desire to preserve Thomas Pynchon's prose, which is nearly identical to Sortilège's narration.

Reese Witherspoon filmed all of her scenes in four days. Writer and director Paul Thomas Anderson loved working with her so much that he and Joaquin Phoenix, who famously worked with Witherspoon in Walk the Line (2005), began talking with Witherspoon about possibly changing the story so that her character would be around more. However, ultimately the actress convinced the two that it wouldn't be a good idea, something that in retrospect Anderson agrees with.

Robert Downey Jr. was originally attached in the lead role, but Joaquin Phoenix ended up taking the role due to Paul Thomas Anderson deciding he wanted to work with Phoenix again. Downey reported that Anderson thought he was "too old" for the role, essentially, not because of scheduling conflicts.

According to Josh Brolin, he and Joaquin Phoenix shot several versions of the progressively weird moments between their characters, which were crazier and crazier, so Paul Thomas Anderson had options when editing the movie.

Thomas Pynchon: Fuelled by comments Josh Brolin gave to the New York Times, rumors persist that notoriously reclusive author is somewhere in the film, which would be the first time Pynchon has been willingly publicly photographed since the late 1950s. The most common theories are Pynchon appears as one of the following: the patient being served soup by a shaky patient in the Chroskylodon Institute (this is actually an actor named Charley Morgan), a dentist in the scene at Golden Fang Headquarters, or the man who passes by the window behind Doc (Joaquin Phoenix) and Coy (Owen Wilson) as they talk at the Spotted Dick party.