Sexual addiction earns a big-screen discussion that is equal parts serious and silly in "Thanks for Sharing," a sober-minded dramedy from the screenwriter of "The Kids Are All Right."

The serious side spins out of the struggles of Adam (Mark Ruffalo), a 12-step devotee who walks the straight and narrow, prays and is never more than a phone call away from his stern, no-nonsense sponsor, Mike (Tim Robbins).

‘THANKS FOR SHARING’ Rated: R Opens today at Kahala 8

The silly stuff comes from the comic struggles of Neil (Josh Gad), an addict who pays lip service to 12-step dogma but who cannot stop bumping into women on the subway or leering at every woman he sees on the streets of New York — a veritable minefield of legs, short skirts and cleavage.

"Is it me, or is Manhattan just one big (bleeping) catwalk?"

Adam is five years sober, careful to avoid the Internet and even TV, doing all he can to purge his life of the sexual temptation that so permeates modern culture. Titillating magazine ads, taxi TVs with leotard-clad workout commercials, buxom billboard models — how can he keep it together?

Then he meets the adorable and gorgeous Phoebe (Gwyneth Paltrow) and the sparks fly. She confesses her "big secret" straight away: She survived breast cancer. He hides his, especially after she confesses that she could never get involved "with an addict" again.

Contractor Mike’s addictions appear to have been many, which is why he struggles and fumes through each day, spouting self-help aphorisms as he does.

"Feelings are like children. You don’t want them driving the car, but you shouldn’t stuff them in the trunk, either."

Neither man has much time for Neil, an emergency-room doctor with mommy issues (Carol Kane), given to inappropriate jokes, thoughts and behavior. But when he’s at the 12-step meeting, he has an honest moment, and that touches fellow sex addict Dede (pop singer Alecia "Pink" Moore).

Paltrow’s Phoebe is the surrogate for the audience here, the person who asks our questions, who doesn’t quite buy this "addiction." ("That’s just what guys say when they get caught, right?")

But the all-inclusive 12-step meetings, filled with testimonials from drug, booze, gambling and sex addicts, take pains to treat this malady as seriously as the more accepted forms of addiction.

The movie lurches between weepy, tragic moments and laugh-out-loud ridicule. Adam struggles; Mike cannot figure out how to stop judging his addict son (Patrick Fugit). And then the sexy, promiscuous and tattooed Dede tests Neil. And as they lean on one another, you start to appreciate the idea that addiction is something you can’t beat alone, by simply "white-knuckling" it.

Ruffalo and Robbins give the film its heart, repeating the encouraging mantra "You’re coming back" after each addict shares how his or her day went. I love the pains that the movie takes to show that we’re all dealing with something — illness or "issues" that eat up our potential. Paltrow and Ruffalo have such great chemistry that their characters are a study in how fragile relationships can be.

But "Thanks for Sharing" is a bit of a head-snapper in its tone changes, stumbling into flippancy. The light moments are appreciated, but they do tend to undercut the sobriety of it all.

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Review by Roger Moore