Heaven Knows What, the new film by College of Communication alums Josh and Benny Safdie, earns its R rating for, as the New York Times describes it, “drug use throughout, pervasive strong language, disturbing and violent images, sexuality and graphic nudity.”

Opening today at the Kendall Square Cinema, the Safdie brothers’ film is a gruelingly realistic drama about the lives of homeless young heroin addicts on Manhattan’s Upper West Side, played mainly by nonactors, some of whom are in fact young heroin addicts on Manhattan’s Upper West Side. Like the lives of the addicts, which consist largely of scoring, shooting up, stealing, and panhandling, the film is sometimes hard to watch, and at times seems to be going nowhere. But there’s grim drama to come.

Heaven Knows What is the story of Harley, a washed-out blond of 19, played by Arielle Holmes, who is hopelessly in love with the handsome but nasty Ilya, played by Caleb Landry Jones. As the movie opens, Harley is working up the nerve to comply with his sneering suggestion that she kill herself. The script is closely based on the life of Holmes, who really did try to kill herself, while the life of the model for the Ilya character is even more tragic: he died of an overdose this past April.

“That was hard for all of us, and as you can imagine, especially hard for Arielle,” says Josh Safdie (COM’07), who cowrote the film with Ronald Bronstein and directed it with his brother, Benny Safdie (COM’08).

The filmmakers say the most important thing about making the movie was that Holmes was satisfied with the way they told her story. “This was really her movie,” Josh says. “We ran everything by her, every casting decision, every art department decision.”

After the shoot, the filmmakers paid for Holmes to complete rehab.

The Safdies found critical success with their films The Pleasure of Being Robbed and Daddy Longlegs, which premiered in the Cannes Film Festival Directors’ Fortnight sidebar in 2008 and 2009, respectively, and with the documentary Lenny Cooke at the Tribeca Film Festival in 2013. Their films Daddy Longlegs, Heaven Knows What, The Pleasure of Being Robbed, and The Safdie Brothers Short Films are being shown at the Champs-Elysées Film Festival, held in Paris June 10 to 16, where the brothers Safdies appear alongside one of their heroes, director William Friedkin (The French Connection, The Exorcist).

Bostonia spoke with Josh Safdie from his home in Harlem as he was packing for France.

Arielle Holmes stars in the Safdie brothers’ film Heaven Knows What, based on the raw details of her life as a homeless addict in New York City.

Bostonia: Why did you make this film?

Josh Safdie: We were in a really weird spot. We had spent the better half of the last three years writing and prepping and doing insane research for this other film, Uncut Gems, on the Diamond District, which was going to be our big movie. We wrote the script together and we were dead set on making it, and it was proving to be really difficult to make that movie with the talent we had attached to it. It was very stressful, very frustrating.

About a year into it, when I was doing research in the Diamond District, I met Holmes. I thought she was incredible. I saw her going into the subway, and she wasn’t like a homeless girl at all; she was dressed very nicely. And I said, “I would love to find a role for you in this movie.” I didn’t realize she was going to her methadone clinic. And then I met up with her a week later, and all the truths and details of her life came out almost immediately. I just kind of became her friend. I’d see her about once a week. About two and a half months into it, I got her a job, and she didn’t show up for the job—she was in the hospital, because she tried to kill herself.

How did you persuade Benny to make the film?

At first, I couldn’t convince Benny and our other partner, Ronnie Bronstein, to creatively invest themselves in it. I was like, “I’m telling you, there’s something unique about this girl, the way she carries herself, the way she speaks, the way she is.” So then I commissioned her to write about her life. I paid her per page, and that turned into a book. And the goal was to turn that book into a movie, cast her as the lead, and basically re-create the past 18 months of her life, condensing it down into about a 3-month span. It’s not 100 percent real life. We’re basing it off of people and mixing things for drama’s sake.

This must have been an especially challenging shoot, with a cast of mostly street people, some with serious drug problems.

If I think, wow, this movie is so easy to make, I most likely would not be making a good movie. I think goals are achieved when you have obstacles to overcome. And yes, there were unbelievable obstacles. Even the way we had to fund it was unconventional. We were making a movie where one of the lead actors had multiple warrants, so he’s on the run, so at any moment we could wake up and he could be in jail for a year. So each day it was discussed: do we have a movie if he were to get arrested tomorrow?

A lot of Heaven Knows What is tough to watch. There were so many challenges, and it was risky. Why was this movie so important for you to make?

Why was I so attracted to this world? Why did I want to get so close to it, and why I am still so close to a lot of it? I don’t know. I’ve been that way for as long as I can remember. I just felt that burning desire to share this story, the fact that it was so romantic and so unbelievably horrific. I recently came to this realization that romance and horror are hitting the same beats, just one of them is usually more excusable than the other. It was this world that exposed that to me.

What is happening with Arielle’s book?

There was a proposal to publish it as a kind of scrapbook when the movie came out, but she wasn’t really supportive of that way of doing it. Now there’s another, really serious publisher interested. The chapter that inspired a lot of the movie was called “Ilya”; it was like an 80-page chapter. And now she’s going to go back and take those 80 pages and flesh them out and really work on them with an editor and turn that into the book. The goal is for it to come out in early 2016. There’s no contract signed yet. She’s acting in Andrea Arnold’s (Wuthering Heights, Fish Tank) film now, and that’s pretty all-consuming.

What parts of your BU education still resonate as you make movies?

We had a teacher, Ted Barron—he’s no longer there, he’s at Notre Dame now—but he uprooted all of the snotty-nosed teenaged wisdom I brought to film school. He asked this question on the first day of class: “All right, everybody think about this and write it down. Who’s in control, the actor or the director?” And I think 90 percent of the class wrote “director,” and I wrote, “I’m not sure,” and a conversation ensued. And now what I’m learning, on the street at 3 in the morning with Arielle, when she didn’t intellectually agree with the way we were directing, what did she do as the real authority in the situation? She gave us absolutely zero, and she knew we wouldn’t be able to use it.

Heaven Knows What opens Friday, June 12, at the Kendall Square Cinema, One Kendall Square, at 35 Binney St., Cambridge.