Just last year, audiences came to know Timothée Chalamet, 22, through his Oscar-nominated role in the tender gay romance Call Me by Your Name. This year, his big starring vehicle isn’t quite as soothing.

Chalamet plays spiraling drug addict Nic Sheff in Felix van Groeningen’s Beautiful Boy, the harrowing drama based on the memoirs of Sheff and his father, author David Sheff, played by Steve Carell. Shifting between a relatively carefree childhood and an adolescence marked by helplessness, the film observes Nic’s downfall through his father’s eyes. Rather than provide a neat arc toward recovery — as Hollywood has tended to do — Boy is propelled by relapses, estrangements, death scares, and the increasingly difficult decisions Nic’s family needs to make for his care.

Chalamet concedes that the atmosphere on set was “intense” given the material, but he also describes it as “dutiful.” “[It was] more a devotion to getting this story right,” he explains. “With high emotional family stakes at play, you feel a responsibility to the actual story…. We tried to capture someone in the throes of addiction, caught between, addled.”

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In the film, Chalamet embodies the delirium of a meth high and the shakiness of withdrawal with unflinching physical commitment. He’s put through the acting wringer: vomiting, passing out, sobbing until every tear is used up. Hardest to watch, however, is when Nic lies to the people he loves. In one devastating scene, after being estranged for some time he meets his father under false pretenses at a diner in their San Francisco hometown, only to face cold rejection. “You don’t like who I am now,” Nic tells David in a wrenchingly acted moment by Chalamet. “The movie is encompassed in that scene,” Chalamet suggests. “The love between father and son ignores the elephant in the room at first, and then they’re both wholly confronted by it when simple conversation is made impossible. By the end of the scene, I think they are both reeling from their inability to help the relationship, or Nic’s addiction.”

It’s also a scene that showcases the potent chemistry between the film’s two lead actors. The difference in years of experience between them wasn’t lost on Chalamet, who describes Carell’s work as “always honest and real.” He gushes, particularly, about the “moment to moment consistency” of Carell’s performance, from which he realized the importance of “letting things come to you in scenes, and not the other way around.” Yet Chalamet had a larger takeaway from observing his screen partner. “It was also the way [Steve] carried himself on set,” he explains. “He has this kind of incredible combination of humanity and professionalism, it makes you want to be around him and work with him.”

Chalamet credits Oscar-nominated screenwriter Luke Davies (Lion) for creating such a nuanced, compelling character — and for convincing him to take on such a tricky, heavy part without hesitation. “The role was presented [with] a juxtaposing mania,” he says. “This would have made it a dream for any actor to play.” In Chalamet’s hands, it’s impossible to turn away.

Beautiful Boy premieres Sept. 7 at the Toronto International Film Festival, before opening in select cities on Oct. 12. Watch the trailer above, and see an exclusive still from the film below.