To prepare for his role, Colin Farrell shed forty-four pounds (twenty kilograms) to achieve a skeletal-like thin appearance that surprised reporters and close friends. To obtain this look, he reportedly lived on black coffee, Diet Coke, and tuna.
At the age of eighty-six, Sir Christopher Lee had to learn more lines of dialogue for his role in this movie than for any other movie he has done before. His career spanned more than sixty years and over three hundred movie and television productions.
Sir Christopher Lee stated in several interviews that due to his age, this movie would mark the last time he would accept a lead role.
In this movie, Joaquin asks Mark his age, to which Mark replies he is thirty-four. Colin Farrell was thirty-three when making this movie. Joaquin later admits in this movie that he is eighty-six, which was the age Sir Christopher Lee was at the time of filming.
In the second season of True Detective (2014), Colin Farrell appeared with Kelly Reilly. In this, she's the wife of his friend. Kelly played Vince Vaughn's wife in True Detective (2014).