During the first 15 minutes of 6 Balloons, a low-budget drama premiering on Netflix, you’d be forgiven for thinking that you’re actually watching a sprightly hipster comedy. It’s not just the presence of Broad City’s Abbi Jacobson in the lead role but a lightness behind the scene-setting, an easy warmth that lures us in before the rug is pulled from underneath.

Katie (Jacobson) is a slightly nervy control freak trying to corral those around her to organize a surprise party for her boyfriend while resisting the urge to do it all herself. She’s determined for it to be perfect and when her father fails to pick up her brother Seth (Dave Franco), she heads out to get him instead. But when she arrives, she’s greeted with a red flag: his mail has mounted up, unopened. As he gets into her car, young daughter in tow, it becomes clear that Seth has relapsed. He’s a heroin addict whose brief stints in detox have failed to pull him out of the hole he’s made for himself and Katie soon realizes that her carefully constructed party plan for the day is in need of a major alteration.

There’s an involving matter-of-factness about 6 Balloons that makes the escalation of events feel grounded, with writer-director Marja-Lewis Ryan avoiding unnecessary conflict to amp up the story. At 71 minutes, there’s no time for anything extraneous, and while the slim running time does make it feel almost unfinished there’s enough here to distinguish it from other dramas within the addiction subgenre. The naturalistic interplay between brother and sister, complete with darkly funny barbs about the horrifying situation they’re in, means that we’re invested in, if not entirely understanding of, the decision-making that follows.

As the lighthearted quirkiness of the initial scenes fades, we’re soon plunged into nightmare territory as Katie is pulled further into the grim reality of her brother’s predicament, witnessing the sweaty, pleading disgust of his withdrawal and deciding to temporarily alleviate his pain with a fix. It’s in this middle section that the film really flies, a procession of tough scenes that might prove uncomfortable to watch, but they’re portrayed with such raw commitment that they linger long after the film ends.

What’s unusual yet important about the set-up is that here is a portrait of a middle-class heroin addict, surrounded by people who love and support him, at odds with the many portrayals we’ve grown accustomed to, abandoned, penniless and alone. It’s not a film about easy solutions and we’re under no illusions that what we see in the short running time is just a brief chapter in what may or may not be the start of a long road to recovery. Jacobson and Franco, who have both been most associated with their comedic work, have a comfortable chemistry together, veering between fractious tension and loving concern, and they help to flesh out the thinner elements of the film. Jacobson in particular makes a convincing case that she will enjoy a fulfilling career long after the end of Broad City.

There’s a rather ill-advised framing device used throughout that overlays self-help advice, almost like chapter openings, and it feels a bit clumsy and on-the-nose. It feels like a directorial decision made to avoid accusations of it all feeling a bit stagey, given that the film exists almost entirely in one location with the two siblings. At just over an hour, it feels worthy of expansion, but as a short, sharp reminder of the sprawling horror of addiction, it makes its point with a stinging sadness.

• 6 Balloons will stream on Netflix from 6 April