There's a key element missing from the ads, the trailers, and most of the hype and hoo-ha for Love & Other Drugs, and I feel duty-bound to point it out: early-onset Parkinson's disease.

At the heart of this raunchy romantic comedy set in the mid-'90s, with Jake Gyllenhaal as a Big Pharma salesman hawking the wonder drug Viagra to a happy, horny throng, is a Love Story-like bummer. Anne Hathaway's character, a photographer, a barista, a woman who wants sex without attachment, is in the first stages of the degenerative disorder. This, needless to say, complicates matters when it becomes clear that Gyllenhaal's charming cad, Jamie, has fallen for Hathaway's doe-eyed free spirit, Maggie. (He loves those eyes, and those breasts.)

Mixing comedy and melodrama is not a crime. In fact, Judd Apatow, whose influence is all over Love & Other Drugs - to its detriment - pulled off this tricky balancing act (and then some) with Adam Sandler in Funny People. But on some level, the marketing deception perpetrated by 20th Century Fox, and perhaps complicitly by filmmaker Edward Zwick, isn't simply a matter of hoping not to scare people away. It shows a fundamental lack of faith in the material at hand, and also a lack of command. There's no adroitness, no grace in the handling of the pitching emotions - funny, sad, icky - that such a story presents.

So, in addition to misleading ticket buyers, Love & Other Drugs becomes, as it proceeds, terribly askew in tone: masturbation jokes and homemade sex vids one minute, a teary group testimonial by Parkinson's patients the next.

It's easy to see why Zwick, who once upon a time profiled yuppie commitment-phobes in About Last Night (Demi Moore and Rob Lowe, egads!), was interested in the rise, so to speak, of Viagra and the pervasiveness of pharmaceuticals. This is firm material, so to speak (I'll stop, but Hathaway doesn't: She lets loose a whole cute flurry of erectile-dysfunction-drug puns). It's not just medical, it's cultural. Drugs for sex, drugs for moods, drugs for sports, drugs for weight loss - Big Pharma sells its wares like the Big Three sell their automobiles.

That slick, profit-driven ethos is addressed, with varying degrees of success, in Love & Other Drugs as Jamie and his cocktail-swilling mentor (Oliver Platt) tote bags of samples around doctors' offices, wooing the support staffs, handing out pens and umbrellas; at a Pfizer motivational rally, where the snappily attired sales force are christened "fully qualified health care professionals," and in the shots of a busload of senior citizens (just in case you miss that fact, the bus sports a "Senior Citizens" sign) heading for Canada to fill prescriptions because they can't afford the prices at home. (Where's Michael Moore when you need him?)

Gyllenhaal and Hathaway strike a certain kind of chemistry, and they've let themselves be filmed naked and entwined, coital, postcoital, smitten, and, as the Parkinson's business takes over, filled with dread. The idea of having two people surrender to love when both professed more sober intentions is the stuff of a thousand rom-coms, and at least these two stars bring wit and spark to theirs.

But Zwick and his cowriters (Marshall Herskovitz and Charles Randolph) are constantly letting Gyllenhaal and Hathaway down. Jamie's big "I need you" speech, after he has chased Maggie down at an interstate rest stop, is pitifully flat. Gyllenhaal stands there, eyes wide with earnestness, gesticulating, spouting cliches.

And the less said about Josh Gad, who plays Jamie's chubby, romantically challenged, porn-junkie brother, the better. Suffice to say that Gad's callow dude is to Zwick and his movie as Jonah Hill is to Apatow and his pictures - the insufferable, sex-on-the-brain man-boy there to supply moral contrast and comic relief.

So is Love & Other Drugs the date flick of the season? Maybe. But audiences are just as likely to rush home afterward and check WebMD for Parkinson's symptoms as they are to light up the scented candles and turn the lights down low.

Contact movie critic Steven Rea at 215-854-5629 or srea@phillynews.com. Read his blog, "On Movies Online," at http://www.philly.com/philly/blogs/onmovies/