Let’s get this out of the way: The only thing Friends With Benefits and Natalie Portman’s No Strings Attached have in common is that they’re both romantic comedies about friendships with casual sex. In terms of supporting characters, plot details and, yes, success as a movie, the two are notably different. No Strings Attached is a better, funnier film, whereas Friends With Benefits has some amusing moments before getting weighed down with a serious tone.

Fresh off an amusing breakup with an un-credited Emma Stone, Dylan (Justin Timberlake) flies from L.A. to New York City for a job interview. At the airport he’s greeted by the smokin’ hot Jamie (Mila Kunis), herself coming off an amusing breakup with a credited Andy Samberg. Jamie is the corporate headhunter who got Dylan his interview, and the two immediately hit it off. “I’m going to change your life,” she tells him in the year’s most obvious line-with-a-double-meaning, and indeed she does. She sells him on NYC, he takes the job, and a beautiful, platonic friendship is born.

All is well until they watch a tacky romantic comedy together, the kind that is so cheesy and saccharine that it would make you throw up if it actually existed. Thankfully Jason Segel and Rashida Jones play the couple in the movie-within-a-movie, and they perfectly understand how to mock convention. In fact, a movie starring Segel and Jones mocking rom-coms probably would’ve been more amusing than Friends With Benefits, if only because Benefits tries to mock the rom-com formula but woefully falls prey to it in the end.

Back to Dylan and Jamie. Disgusted by the fictional storybook love they see in the movie, they ask why relationships have to be so complicated. (Short answer: Because they are!) They then swear on an iPad Bible that they’ll have “no relationship, no emotions, just sex” and vow to remain friends no matter what. Yeah, right. Haven’t they seen romantic comedies?

Director Will Gluck’s (Easy A) film is at its best when Dylan and Jamie are trading barbs and hooking up—their chemistry feels real, and there are good laughs to enjoy. Dylan and Jamie know one another’s tendencies and weaknesses, play practical jokes on one another, and have no trouble telling one another the truth. If anything they’re better friends than they are lovers, but of course we need to like them as friends and want them to be together in order for the movie to work. We do like them, but the movie still doesn’t work.

Timberlake holds the screen adequately as a co-lead, but he’s also helped greatly by Kunis’ presence, timing and experience. His future as an actor remains bright but unproven. And clearly if the story stayed focused on comedy, Timberlake would’ve been better off, but unfortunately Dylan and Jamie’s inevitable fight nearly turns the film into a Nicholas Sparks (Dear John) drama. It gets so heavy that we stop laughing and start rolling our eyes waiting, begging for it to end.

Aside from the love/hate relationship drama, which we expect, there’s also mental illness and dysfunctional family drama, which we neither expect nor want. Jamie’s mom (Patricia Clarkson) is an unreliable floozy who doesn’t know who Jamie’s father is, and Dylan’s father (Richard Jenkins) has Alzheimer’s while his sister (Jenna Elfman) is a single parent to young Sam (Nolan Gould). Where did all the laughs go?

Worse, not all of the comedy connects. Timberlake singing Kris Kross’ 1992 hit “Jump” is no doubt funnier on paper than in execution, as is having Olympic snowboard gold medalist Shaun White in a cameo in which he’s a jerk to Dylan. “Ha! That Shaun White is cool for making fun of himself,” we’re supposed to say. But we really just feel sorry for him.

Friends With Benefits tries to make fun of rom-com conventions and then subvert them, all with the intention of finding a different path to ending where all rom-coms end. It’s a nice idea, but when you veer too far off course everything is bound to crumble, and it does.

Friends With Benefits HH • Directed by Will Gluck • Starring Mila Kunis, Justin Timberlake, Patricia Clarkson, Jenna Elfman • Rated R • 109 min • At Century Cinemas Del Monte, Maya Cinemas, Northridge Cinemas, Lighthouse Cinemas.