The actor plays the 21-year-old title character who has an unnatural attachment to his mother, played by Marisa Tomei, and he admits it was a "stretch" from his normal comedic parts.
He tells Britain's Total Film magazine, "It's definitely more of a dramatic stretch for me. I'd say it was the first time ever it was difficult to go home at the end of the day and shake off what I was doing earlier in the day and just hang with my friends or girlfriend and be normal after playing such a severely affected guy."
But he is glad he signed up for Cyrus - because it has won him even more dramatic roles.
He adds: "Bennett Miller, who directed Capote, saw this movie and cast me as the second lead in a baseball drama called Moneyball that stars Brad Pitt, Philip Seymour Hoffman and Robin Wright. Cyrus already has done more than I could have imagined in that regard."