Dale Denton (Seth Rogen, left) and Saul Silver (James Franco) are stoners running for their lives in the action-comedy Pineapple Express. (Sony Pictures)

There were two good reasons to have high hopes for the Judd Apatow-produced drug comedy Pineapple Express: a) it was written by Seth Rogen and Evan Goldberg, who gave us last summer’s surprise hit, the raunchy-sweet Superbad; and b) it was directed by David Gordon Green (Snow Angels, All the Real Girls and George Washington), a talented young filmmaker with a sensitive touch.

As it turns out, neither the writers nor the director seemed quite sure what they were trying to do with this movie. It doesn’t really matter. They’ve still managed to craft a loose, giddy little comedy, anchored by a beautifully blissed-out performance from James Franco, who is so deliriously funny that, like a few hits of good weed, he’ll leave you giggling helplessly.

The film stars Rogen as Dale Denton, a process server who enlivens his distasteful job by using disguises when delivering divorce papers, subpoenas and the like. He also manages to float amiably above the angry recipients of his deliveries by staying permanently high. Keeping him in weed is Saul Silver (Franco), a grungy, long-haired, sleepy-eyed dude who deals out of his cozily cluttered crib. Despite his sucky job, 25-year-old Dale isn’t a total loser. For one thing, he’s dating a hottie named Angie (Amber Heard). (She also happens to be a high school senior – shades of Manhattan.) When Angie wants Dale to meet her parents, he prepares himself for the dreaded occasion by dropping in on Saul for a fresh supply.

Saul just happens to have gotten his hands on some extraordinary stuff: “The dopest dope I ever smoked,” he assures Dale. It’s a supernal strain of marijuana dubbed Pineapple Express, a nod to the moist airflow from Hawaii that feeds it. A lyrical Saul makes it sound like the Holy Grail of highs. “It’s almost a shame to smoke it,” he intones reverently, fixing Dale with his red-rimmed eyes. “It’s like killing a unicorn.” Dale buys the pot and quickly leaves, despite lonely Saul’s pleas that he stay and hang out. (In a funny-sad twist, it’s not the user who is needy in Pineapple Express but the pusher.)

From left, potheads Dale, Saul and Red (Danny McBride) discover that where there's smoke, there's fire. (Sony Pictures)

Dale should have listened to Saul. Instead, he drives to his next assignment and is sitting outside in his car, smoking some of his new stash before serving the papers, when he accidentally witnesses a murder. Dale flees in a panic but not before being spotted by the killer and fatefully leaving behind a smouldering roach. It turns out the killing was part of a local drug war and Dale has just seen the kingpin, Ted (Gary Cole), bump off one of his Asian rivals.

Thanks to the rarity of Pineapple Express, Ted and his minions can easily link the discarded roach to Dale. A frantic Dale heads back to Saul’s apartment, and soon, the two of them have grabbed a few dope necessities – rolling papers, munchies – and are on the run.

Pineapple Express starts out as a slightly more sophisticated variant on the classic stoner comedy. There’s even a bit of confused byplay as Dale tries to enter Saul’s apartment building that pays homage to Cheech and Chong’s most famous routine. About midway, however, Pineapple Express starts to morph into a spoof of buddy action flicks, replete with gunfights, car chases and litres of spilled blood. It seems the filmmakers weren’t entirely certain what genre, or tone, they were going for. As a result, neither are we. Dale has an epiphanic moment when he realizes being high all the time may be a problem, but the film doesn’t follow up on that revelation; a subplot in which Angie and her parents get drawn into the drug war just fades away. Writers Rogen and Goldberg, following their Superbad formula, alternate raucous slapstick with quieter moments of acutely observed character comedy, but this time, violence knocks things out of balance.

Regardless, I’d watch this movie again just to savour Franco’s portrayal of the sweetly addled Saul. With his grubby clothes and stringy hair, Franco’s lotus-eater looks like he’s auditioning for a Nirvana cover band. But there’s no Cobain-style angst here: Saul is so chill, he moves as though he were under water. And his brain works in slow motion, too. The scenes in which he and the dazed Dale try to strategize their escape are hilarious; the film has more sly comic fun with the debilitating effects of dope than the goofy Harold and Kumar movies. At the same time, Saul may be the screen’s first wholly lovable drug dealer – a good Jewish boy, he pushes the stuff to pay for his bubbe’s retirement home. Franco’s Saul is to Pineapple Express what Michael Cera’s Evan was to Superbad – a gentle spirit who offsets the movie’s coarser jokes and characters.

Drug lord Ted Jones (Gary Cole, left) teams up with crooked cop Carol (Rosie Perez) in Pineapple Express. (Sony Pictures)

Rogen, meanwhile, gives us another version of his Knocked Up character. Dale Denton may be slightly less of a shmuck than Knocked Up’s Ben Stone – this guy didn’t get a foxy blond girlfriend by accidentally impregnating her – but he’s still awash in self-doubt. Most of the time, though, he plays straight man to Franco and to Danny R. McBride as Red, Saul’s kimono-clad supplier. McBride is amusing, but the late addition of a third wheel is another sign of this buddy comedy’s jerrybuilt plotting. To go back to Superbad, McBride is no McLovin.

The supporting cast is uneven. Cole has his moments as a boozy drug lord who gets his buzz from beer; his partner in crime, a crooked cop, is played with brio by the ever-feisty Rosie Perez. But Kevin Corrigan and Craig Robinson, as a pair of henchmen who look like Neil Diamond and Mr. T, are never quite as funny as they’re intended to be.

Whatever. If nothing else, Pineapple Express does one great thing: it exposes the comic gifts of James Franco, hitherto best known as bad boy Harry Osborn in the Spider-Man movies. To paraphrase Saul’s scrambled words of wisdom, once you’ve let Pandora out of her box, you can’t make her go back in.

Pineapple Express opens Aug. 6.

Martin Morrow writes about the arts for CBCNews.ca.