In “Beautiful Boy,” the national epidemic of substance abuse is told in intimate personal terms. An unembellished portrait of present-day addict life, it explores the chilling real-life struggles of journalist David Sheff and his teenage junkie son Nic. Adapted from their joint memoirs, it offers a stomach-churning primer of addiction’s traumatic effects on individual and family lives. It is not a movie for the faint of heart, but one that will stick long in your mind.

The focus isn’t the drug trade that traffics in addiction, but the chaotic consequences it brings to once-loving relationships. Beginning in mid-catastrophe, it shows a grieving, bewildered David (Steve Carell) asking a clinician to explain how powerful addictive drugs affect users.

Though he has written for the likes of Rolling Stone and the New York Times, he’s not researching an article. He is trying to comprehend what happened to Nic (Timothée Chalamet), whom he raised in a loving rural Northern California household. A decade earlier, David told his warm, intelligent boy, “I love you more than everything.” Now he scours San Francisco’s alleys and emergency rooms to find a young man he still treasures but no longer trusts.

Nic’s downward spiral to a deceitful virtual stranger is the film’s tragedy and mystery. With fleeting transitions and loosely constructed narrative vignettes, Belgian director Felix Van Groeningen carries us across several years of Nic’s exposure to illicit drugs.

It begins with a joint that he persuades his surprised, strait-laced father to share as they celebrate his being accepted to each of the half-dozen colleges where he applied.

From that cheerful beginning, the charismatic Nic moves into a busy, demanding campus world that seems subtly inhospitable. With abundant nervous energy and tiny nervous tics, he finds temptations no farther away than prescription drugs innocently kept in bathroom medicine cabinets.

What follows is a cycle of occasional hopeful highs, miserable downs and the camera staring unblinkingly as injection needles slowly but surely enter veins.

Carell and Chalamet have palpable chemistry together and deliver fearless, stellar performances. The film neither sympathizes nor judges the characters and offers no easy resolution. David forlornly comes to see Nic’s addiction as a rotten hand that he dealt himself, a hardship that parental concern can’t do much to reverse.

But Chalamet’s understated transformation from promising, vivacious country boy to heroin-addicted hustler is the highlight of the film. His Nic is the sort of fallen angel that becomes a demon.

He offers halfhearted attempts to go clean, but he’s really living for the next hit. His notebook, filled with garish horror drawings and morbid journal entries, suggests the fatalistic state of mind he has been trying to escape. He’d rather live on the edge, more excited about finding the next score than the means to survive. At times it seems that he thinks the best high of all would be death.

There is a sense of repetitiveness in this strikingly low-key film that is almost inevitable, given its subject. Staying clean is harder and less satisfying than anyone anticipates.

Nic plays the love card with his father when he might be able to get a few hundred dollars in the process. David’s attempts to halt Nic’s self-destructive impulses follow similarly pointless paths. This is a drama built of harsh realities that are powerful enough to offset its slow pace and audience-manipulating pop soundtrack.

It’s not as though we lack awareness about the drug catastrophe. It’s a perennial subject for cinema. Filmmakers have been criticizing, glamorizing and exploring it since the art form arrived. Still, for those who lack firsthand experience of cycles of destructive habits and despair, recovery and relapse, this should be a compelling wake-up call.

“BEAUTIFUL BOY”

***

(R, 2:00)