By turns intensely naturalistic and brutally stylized, “6 Balloons” mercilessly turns screws and escalates dread while spinning a worst-case scenario about the fraying family ties between a heroin addict, who’s chronically incapable of curbing his self-destructive appetite, and his sister, who’s buckling under the weight of the latest in a long series of his impossible demands.

Writer-director Marja-Lewis Ryan drew upon the real-life experiences of producer Samantha Housman while developing her edgy scenario, and audaciously cast in the lead roles two actors best known for their work in comedy — Abbi Jacobson (of “Broad City”) and Dave Franco. The movie leaves you with a deep respect for the willingness evidenced by Ryan and her collaborators to take several gambles that pay off dramatically and emotionally. But be forewarned: If your own experiences mirror in any way what unfolds in “6 Balloons,” it also will leave you more than a little bruised.

Katie (Jacobson) is busy preparing a surprise party for her boyfriend, with the help her mother (Jane Kaczmarski) and father (Tim Matheson) and a coterie of close friends, when she notices that her brother Seth (Franco) and his toddler daughter Ella (played alternately by twin sisters Charlotte and Madeline Carel) are late in arriving. When she can’t reach Seth on his cellphone, it’s easy to read in her worried expression that she knows what that probably means. So, using the pretext of running out for a birthday cake, she drives over to his apartment, where she immediately notices that Seth hasn’t been picking up his mail. She knows what that definitely means.

Sure enough, Seth has been using again. At first, he claims he hasn’t, but Katie won’t buy it, and their give-and-take sounds unmistakably like a conversation they’ve had a zillion times before. Indeed, Katie already has come to fear she may be dragged down by her brother into his private corner of hell. She wants to “let go with love,” as she’s encouraged by the self-help audiotape she plays in her car throughout the movie. (That may sound like a heavy-handed touch, but be patient: It builds to something powerful.) She wants to stop being Seth’s enabler. She wants to save herself.

But, of course, she acquiesces when he asks her to take him in for detox.

“6 Balloons,” which will start streaming April 6 on Netflix, clocks in at a tight 74 minutes. But it feels as though it’s gradually expanding to the enormity of a wide-awake nightmare as it follows Katie and Seth — and, in the backseat, Ella — along a circuitous L.A. roadway paved with good intentions and desperate measures. Stops along the way include a frustrating visit to a clinic that won’t accept Seth’s insurance; a paranoia-ratcheting side trip to an inner-city marketplace for unprescribed medications; and a near-closing-time interlude in the bathroom of a drug store, a sequence both darkly comical and grippingly suspenseful as Seth and Ella simultaneously require attention while a disapproving pharmacist (Heidi Sulzman, making every second count in a fleeting role) hovers nearby.

You can’t help feeling that something terrible will happen at any moment, unless something worse happens first.

A textbook example of pared-to-essentials storytelling, “6 Balloons” tells us only what we absolutely need to know about Katie, Seth and their shared history, and requires us to infer just about everything else. Fortunately, that task is made appreciably easier by the remarkably exact performances by Jacobson and Franco.

Jacobson speaks volumes with anxious body language and quicksilver changes of expression, so that, even on those occasions when Seth appears cheery — maybe a little too aggressively cheery — Katie’s smile is merely tentative; obviously, she knows from experience that things can turn poisonously sour in a heartbeat. Franco persuasively plays Seth as an indulgent weakling who only partly camouflages his skills as a crafty manipulator. His mother and father have grown immune to his dubious charms, but he knows (or, to be more precise, hopes) that his sister remains an endless source of sympathy.

Ryan, who first attracted notice in 2010 by writing and co-starring in “The Four-Faced Liar,” a well-received, sexually flexible romantic comedy, never attempts to emulate Seth’s stealthiness here. From the opening minutes onward, she makes it clear that “6 Balloons” actually is a drama about two people straining to break free of crippling addictions. Perhaps the riskiest move she makes in the entire film is symbolically visualizing Katie’s struggle in a manner that could have come across as inadvertently comical. But she pulls it off, and the movie is all the more potent for it.

SXSW Film Review: ‘6 Balloons’

Reviewed at SXSW Film Festival (Narrative Spotlight), March 13, 2018. Running time: 74 MIN.

  • Production: A Netflix release and presentation of a Campfire production in association with Free Association. Producers: Samantha Housman, Ross M. Dinerstein, Channing Tatum, Reid Carolin, Peter Kiernan. Executive producers: Ian Bricke, Lynette Howell Taylor.
  • Crew: Director, Screenplay: Marja-Lewis Ryan. Camera (color): Polly Morgan. Editor: F. Brian Scofield. Music: Heather McIntosh.
  • With: Abbi Jacobson, Dave Franco, Charlotte Carel, Madeline Carel, Maya Erskine, Dawan Owens, Jen Tullock, Lisa Bierman, Pierce Minor, Heidi Sulzman, Tim Matheson, Jane Kaczmarski.