Jared Leto is no stranger to dramatic transformation.

He has taken on many faces throughout his acting career, including a teenage heartthrob in the 1990s TV series "My So-Called Life," famously losing 25 pounds for his role as a drug addict in 2000's "Requiem for a Dream" and then gaining 60 pounds in 2007 as he became overweight and unrecognizable while portraying John Lennon's killer in "Chapter 27."

He has done it again. Talking about his first movie role in six years, Leto, 41, reveals why he took on the part of Rayon, a transsexual woman with AIDS, in the new film "Dallas Buyers Club."

"I did it because I fell in love," Leto told ABC News. "I fell in love with the role."

In order to accurately portray the role of Rayon, a dying drug addict, Leto lost a shocking 30 pounds, which is nearly one-third of his body weight, shaved his eyebrows and waxed his legs.

"It was a necessity," he said. "I was playing someone who was addicted to drugs and also dying of AIDS."

He wasn't the only actor in the film to undergo dramatic transformation, however. An equally emaciated Matthew McConaughey plays the role of Ron Woodroof, a hard-living homophobic electrician who contracts HIV in 1986 and eventually teams up with Rayon, importing and distributing anti-viral medications.

Leto was so dedicated to his role, he said, he stayed in character the entire time they were shooting the movie, even when he was completely alone.

"It was pretty hard to leave that role," he said.

It wasn't until the film's premier that Leto finally met his co-stars completely as himself, which happens to be an almost full-time musician, releasing critically acclaimed albums and touring the world with his rock band, 30 Seconds to Mars, for which he's the lead singer.

"It wasn't supposed to be successful, you know?" Leto said of his music career. "But lo and behold, it did become that."

And for now, it seems movies are on the sideline for him.

"I don't know how long it's going to be until I make another," he said, adding he has no other films in the pipeline.