In September 2010 director Casey Affleck confirmed that this movie is not a real documentary, but fake. The public had been wondering ever since Joaquin Phoenix announced in October 2008 his retirement from acting in order to become a rapper, whether it was all just an act or if it was for real.
Towards the end of the movie, there is a scene where Joaquin Phoenix is sitting with his father, at a table, drinking beers. In reality, this man is not Joaquin Phoenix's father, but actually Casey Affleck and Ben Affleck's own real-life father.
In the defecation scene, where Joaquin Phoenix gets pooped on in bed, the "feces" was actually a combination of humus and coffee grounds. The mixture was inserted into a tube that was taped onto Antony Langdon's (Anton) back that went down to his butt.
In September 2010, Casey Affleck was sued for sexual harassment by producer Amanda White and cinematographer Magdalena Górka. The incidents supposedly occurred during their work together on this movie. The cases were settled.
The final sequence in the film, where Joaquin Phoenix is trekking through the river, was actually longer in the original cut. It was almost another three minutes longer, but Casey Affleck thought that it was "beating a dead horse" at that point and decided to cut it shorter, and that is what we see in the final film.
In the scene where Anton is playing the piano and singing a song (the scene between calling the prostitutes and them actually coming), the shot in the film was actually the third take. Also, the song being sung was written by Anton's brother, and he (Anton) is singing it in a different pitch in the film.