You ever see a movie try to be a lo-fi Lethal Weapon … on weed? Oh, there’s some crazy stuff, man. There’s Seth Rogen in the bushes. Has he got a gun? I dunno! Red team, go! Red team, go!

Marijuana-flick fans will recognize that paraphrasing from Half-Baked — a stoner comedy that realized cinematic laughter can’t survive on herb alone. People smoking, coughing up lungs and giggling isn’t enough. There’s got to be inventive, light absurdity — a gateway to a relaxing high, not the manic-depressive kind in Pineapple Express, where the jokes dissipate long before smoke.

Forget the puff-puff. Just pass on most of this problematic, protracted action-comedy, starring Rogen and a riotous James Franco as burners on the run from murderous criminals and cops.

Last year, co-writers Rogen and Evan Goldberg turned in the touching, hilarious Superbad. They’ve moved on from a labor of love to something laborious which, for all its bloodletting, bullets and blown-up barns, feels far less dangerous than a potentially fractured friendship in Superbad.

Rock-’em-sock-’em ridiculousness of Steven Seagal films, a winking tone a la the far-superior Hot Fuzz and producer Judd Apatow’s usual bro-code credos all vie for attention. None works. An amusing car chase aside, the budget is too limited for much more than overly sadistic, grim gunfights. Such leaden violence never lets the movie reach the lively liftoff of Fuzz. And limp buddy-comedy bits between Rogen and Franco show the frays of Apatow’s funny-friends formula.

Rogen is Dale Denton, a pothead process server who blazes up in his car while darting across town in disguise to slap down subpoenas. Dale blitzes talk radio with opinions; disembodying them is the only way anyone would take him seriously. He’s a 25-year-old slacker with an 18-year-old girlfriend in high school. (Rogen looks 26 going on 32, so it appears even creepier than it sounds.)

Stressed at potentially losing his girlfriend to jocks, Dale visits Saul Silver (Franco), his dealer, to cool out and pick up a few pipes’ worth of Pineapple Express — a rare strain of sweet chiba.

Franco’s work embodies the essence of stoned conversation — hazy thoughts unsustainable from one moment to the next, picking out certain nouns and responding only to those things. Saul’s plans are grander, and weirder, than it seems, and Franco capitalizes here on long-overdue freedom from brooding leading-man parts with one of three performances that save the film from disaster.

Toking on a side street, Dale inadvertently witnesses an assassination. Behind it are corrupt cop Carol (Rosie Perez, wasted) and Ted (Gary Cole, as unfunny as in Talladega Nights), a drug lord who’s supplied Saul with Pineapple Express and traces Dale’s dropped joint to its source.

Saul and Dale wind up on the run from Ted and Carol, fussbudget assassins, Asian cartels, police “liaisons” and duplicitous Red (Danny McBride). Red is Saul’s unreliable cohort, sporting a white-trash perm as resistant to damage as his body proves to be. McBride (as uproarious in the upcoming Tropic Thunder) and Craig Robinson (of NBC’s The Office) as an emotional hitman represent comedic cavalry with a handful of uproarious bits.

Had the film focused on that trio, and trimmed a half-hour, it might have worked. What’s here certainly doesn’t work as a star vehicle for Rogen. He isn’t much fun to watch, better suited to pulling triggers on rapid-fire verbalism than guns in the film’s interminable shootout climax. Rogen has no one to blame for this massive miscalculation of his talent, and director David Gordon Green (known for intimate indie dramas) lacks visual chops to offer little more than bland, bloody beats.

Pineapple Express wants to go out in a cheeky blaze of gory, but there’s just nothing fun about its corpses, crashed-up hatchbacks and charred buildings. It’s obviously meant to be oversized, overemphasized and overblown. After a while, it’s not too much to ask for it to just be over.