If nothing else, Tully should win a prize for the screen’s most realistic portrayal of frazzled motherhood.

Charlize Theron stars as Marlo, a beleaguered pregnant mother of two who falls into post-partum depression with the birth of her third child, Mia. She’s a loving mom, but she’s overloaded with the usual newborn travails: diapers, breast-feeding, pumping, rocking, walking, pleading, sleepless nights. It’s end-of-your-rope exhaustion, and it does things to your psyche.

Marlo shows the pains and strains of her bloated pre- and post-labor body and mind. (Theron gained 50 pounds for the role.) Bringing a new life into the world is not all joy and wonder.

(I’ve never understood why so many films get it wrong. They have the woman with a fake little baby bump, and thin everywhere else, and a perfect-makeup delivery is followed by a perfect-makeup recovery and instant weight loss.)

Marlo’s angst is compounded by juggling her other children, 8-year-old Sarah (Lia Frankland) and 6-year-old Jonah (Asher Miles Fallica), a special needs kid with other yet-to-be-diagnosed issues. Money is tight and child No. 3 was not exactly planned. Her husband Drew (Ron Livingston) travels a lot for work and disappears into video games when he’s home.

Marlo’s mood doesn’t improve when she visits her wealthy brother Craig (Mark Duplass) and his too-perfect wife Elyse (Elaine Tan) in their showplace house that screams consumerism. But Craig has a helpful offer: treating his sister to a night nanny so she can get some sleep and reclaim some sanity.

Marlo resists at first. “I don’t want a stranger in my house,” she says. “That’s like a Lifetime movie where the nanny tries to kill the family and the mom has to walk with a cane at the end.”

But a few weeks later, desperation trumps paranoia, and Marlo welcomes Tully (Mackenzie Davis) into her world.

Tully is a young, vibrant, wise-beyond-her-years life force and everything Marlo thinks she isn’t: thin, pretty, energetic, idealistic, unburdened. She also cooks and cleans.

They become friends and suddenly Marlo’s life has some sense of order. Where all of this is headed is another question. (No spoilers here.)

Tully is the third collaboration between director Jason Reitman and writer Diablo Cody. They gave us the brilliant Juno (with Ellen Page as a pregnant teenager) in 2009, and the not-as-brilliant Young Adult (with Theron as an angry, delusional former prom queen) in 2011. Cody is deft at tapping into the zeitgeist, channeling realistic female anxiety and hurling pithy lines.

Both films focused on quirky, quick-quipping women resisting grown-up responsibilities. Marlo could be both of those lead characters later in life.

Tully is intriguing and quite funny at times, but for all of its realism, this comedy-drama isn’t fully formed. It makes you wish Reitman and Cody had filled in more of the blanks in terms of story and the characters.

What is impressive is Theron’s raw, gritty portrayal. She brings Marlo to life with stark, let-it-all-hang-out honesty. It’s a compelling performance worthy of an Oscar nomination, but I’m afraid the film won’t have enough juice to get her there.

Clint O’Connor covers pop culture. He can be reached at 330-996-3582 or coconnor@thebeaconjournal.com. Follow him on Twitter @ClintOMovies.