Jared Leto was away from movies for five years to focus on his music career before returning to the big screen as a transsexual AIDS patient in Dallas Buyers Club.
But the role required more than learning lines and showing up on the set each day.
'It was intense,' Leto tells talk show host Conan O'Brien. 'I mean I lost between 30 and 40 pounds, was wearing high heels every day... tons of other things as well. I waxed my entire body. My eyebrows included. But it was kind of nice. It was a period piece so I didn't have to do Brazilian, you know?'
The film, which opens on 1 November, stars Matthew McConaughey as real-life Texas cowboy Ron Woodroof who in 1985 was diagnosed as HIV-positive and given 30 days to live.
Bereft of government-approved effective medicines, Woodroof tracked down alternative treatments from all over the world by means both legal and illegal.
Leto's character is a key part of an unlikely band of renegades and outcasts who the entrepreneurial Woodroof joined forces with to establish a hugely successful 'buyers' club.'
'I was in character the entire time we were shooting so I really got to live in the skin of this beautiful creature ... and I really fell in love with her,' Leto says. 'She's the most amazing person filled with life and charm and grace and also addicted to drugs and dying of AIDS. It's an absolutely beautiful story.'
Leto has acted in films sparingly in recent years and instead focused on his band 30 Seconds to Mars. But when he does act, he does commit fully.
For the 2007 film Chapter 27, the actor gained 67 pounds to play John Lennon's assassin Mark David Chapman.
Of his latest transformation for Dallas Buyers Club he says: 'It was a very intense role and challenging but worth it.'