(l to r.) Mackenzie Davis and Charlize Theron in Jason Reitman’s Tully. (Courtesy of Focus Features)

Eleven years after his zany teen pregnancy screwball — a little film called Juno — Jason Reitman is back with a new kind of motherhood comedy. Tully may be less indie-music-infused than its Ellen Page-starring forerunner, but don’t be fooled: this isn’t one of those broad parenting comedies like Mr. Mom, although Reitman wouldn’t be mad if it was.

Mr. Mom is pretty good,” Reitman said at a Tribeca Film Festival talk following Tully’s New York premiere on Thursday. But Reitman’s comedy, which marks his third collaboration with Juno and Young Adult scribe Diablo Cody, is a deeper, darker take on the trials of parenthood. It also serves as a kind of spiritual sequel to the previous two, and Reitman describes the trilogy as “all somewhat autobiographical,” as if he and Cody were “writing this diary together and every five years or so there’s a new entry.”

Tully stars Charlize Theron as Marlo, a droll, somewhat depressed mother of three whose rich brother (played by Mark Duplass) gifts her a night nanny for her newborn. For those of us who aren’t wealthy homemakers, night nannies are exactly what they sound like — babysitters who attend to infants overnight, relieving new parents of the stress and exhaustion induced by having to wake up every few hours and soothe a wailing baby. Enter Tully (Mackenzie Davis): a vibrant, self-assured 26-year-old who takes the reins on supervising the newborn, rescuing Marlo from her misery in the meantime.

One of the joys of the movie is the specificity of its detail, little touches that make the film feel alive and authentic. Most of these were inspired, Reitman says, by his and Cody’s own parenting experiences, as well as those of his friends and crew members. “I’m amazed by the amount of parents who have dropped their phones on their baby’s faces,” he said, referencing an iPhone-slip moment that he added to the film based on stories from his peers.

Another memorable scene finds Marlo pulling a linked string of soiled mini trash bags out of the Diaper Genie, a chore that Reitman recalls from when his own daughter was a baby — though things have changed a little since then. “Diaper Genie’s at like 3.0 now, man. It’s like an electronic thing. It just emails the poop away.”

Still, there’s a certain timeless and universal familiarity to Marlo and Tully’s story, capturing the loneliness and disorientation that inevitably hit at any new stage of your life. “This is something that is very taboo,” Reitman said, “you do not talk about how tough parenting actually is. And how it makes you feel like you don’t know what you’re doing.”

It’s a feeling that’s applicable outside of parenting, too. When he made his first movie, Reitman said, “I had the arrogance of youth.” And on his movies now? “Each time I say, I have no idea how to make a movie. If I once did, I have forgotten. God willing, as I start this process, I will prove myself wrong.”