Abbi Jacobson realizes that her new movie, 6 Balloons, may sound like a fun romp. “I’m kind of nervous that people will be thinking it’s a comedy and they will be thrown,” she says about the film, in which she stars opposite Dave Franco—another actor primarily known for lighthearted work

But Jacobson displays none of the Abbi Abrams’s “yas, queen” clowning viewers have come to expect from the Broad City star in 6 Balloons. Instead, she turns in a subtle and nuanced dramatic performance as the devoted sister of a recently relapsed heroin addict (Franco, also shifting gears) in the Netflix film that begins streaming Friday, April 6.

Jacobson knows the role is quite a departure—and says it took a lot of convincing to get producers to cast her. “I auditioned a couple of times,” she says. “I don’t think I was a lot of people’s first choice, to be honest. [Writer-director] Marja-Lewis Ryan really fought for me.”

The story takes place over the course of a very long day (and night) as Katie, an über-responsible, self-help-tape-listening Angeleno tries to take care of both the last-minute preparations for her boyfriend’s surprise birthday party and her increasingly strung-out brother, Seth—who’s looking after his two-year-old daughter, Ella (Charlotte and Madeline Carel), and desperately needs a detox. Unlike many stories of addiction, this one focuses on the enabler rather than the relapsing addict.

Ironically, one of the producers that needed persuading was Samantha Housman, on whose experience 6 Balloons is based. Rather than being unnerved by the presence of her character’s real-life inspiration, Jacobson says it was “relieving” to be able to check in with her, even though the two women had already spent time together ahead of filming the low-budget indie over the course of 19 days. “Katie has all this anger and frustration and disappointment because she and Seth have been there before, numerous times,” Jacobson says. “I just wanted to make sure I was playing it as real as possible.”

There are some light moments between the squabbling siblings, as when a frustrated Katie tells Seth she wishes he’d told her he’s using again. “Next time,” he says, he will—before waiting a beat and adding, “That was a joke.” Katie’s reply: “No, that was hilarious . . . It brought down the house. You should develop that, like a longer act.” Later, their banter becomes scathing as Katie drives around L.A. looking for a rehab facility—and ultimately, a fix for her brother.