In portraying Lance Armstrong, actor Ben Foster gets into his head — and blood — with “The Program”

This weekend, Lance Armstrong will be thrust once again into a very prominent, public role, this time as the central character of the film “The Program,” a cinematic chronicle of his wild and controversial career.

On Sunday, the film has its global premiere at the 2015 Toronto International Film Festival.

Portraying Armstrong is actor Ben Foster, known to movie audiences, among other roles, as William S. Burroughs in the 2013 Beat Generation biopic “Kill Your Darlings.” Having played the author of Naked Lunch, an artist almost infamously synonymous with heroin at one point, Foster is comfortable with understanding the role of drugs as part of a character. Even for him, though — being an actor who all but embodies the method acting approach of immersing oneself entirely in a role — there can be surprises. Getting into Armstrong’s saddle involved sampling performance-enhancing drugs himself, and the result, Foster said, was entirely unexpected, and utterly unpleasant.

“There’s a fallout,” Foster told the Guardian, a newspaper in the U.K. “Doping affects your mind. It doesn’t make you feel high. There are behaviours when you’ve got those chemicals running through your body that serve you on the bike, but…” In the interview, the Guardian reported, Foster trailed off, shaking his head. It’s as if the experience of performance-enhancing drugs was like nothing he could have possibly expected, even traumatically so.

“I’ve only just recovered physically,” Foster said.

The effects, Foster described, were jarring. Sleeplessness and an anxious excitability, it seemed, were the most prevalent, and for a person who doesn’t spend a majority of his time in the saddle, it was twice as noticeable. “I’m only now getting my levels back,” Foster told the Guardian. “If it’s working, it keeps you up at night. This is losing your marbles, right? They’re definitely rolling around. They’re under the couch, but they’re retrievable.”

His attempt to understand the doping that ended Armstrong’s career, for Foster, was lockstep in line with a method acting approach that didn’t involve mimicking his infamous role, but “infecting” himself with it. Speaking to the Guardian, Foster detailed a number of revelations he made about Armstrong. There were, of course, the drugs — something that required first hand experience, Foster believed. But then there were the more legitimate aspects of Lance Armstrong as a cyclist, even as basic as his riding style. “It was important to get his gait,” Foster told reporters. “I talked to people who had the aerodynamics of his body on a computer system so I could get the hump in the back, the heels slightly out. It’s almost a duck pedal. It’s not a delicate ride. ”

“It’s violent,” Foster suggested, “which is also why he’s such an exciting rider. It’s like he wants to break the bike.” In summarizing what he learned through immersion about Armstrong, Foster describes him as an athlete whose self-belief was as intoxicating as his doping — a belief that strengthened him more than EPO ever could, informing his dishonesty as much as anything else.

“Belief and will got him through, not dope,” Foster told the Guardian. “Had he not been doping, he wouldn’t have won. But his greatest attribute is his ability to believe he’s a winner. That self-righteousness, that self-belief, could be considered akin to acting. It’s not lying, it’s belief.”

The Program premieres at the Toronto International Film Festival this Sunday, and opens worldwide for general audiences on October 16.