Smoked-out films tend to be well intentioned. All “Pineapple Express” wants to do is be as pleasant and funny as a stoner comedy can be. The effort is admirable, and even if it is far from a masterpiece, there’s no way to fault the film for its good intentions.

The movie opens with an admiring ode to its main subject. White-collar worker Dale Denton (Seth Rogen) stops by the apartment of his dealer, Saul Silver (James Franco) to sample a new strain called pineapple express. After Saul tries and fails to keep Dale there as a friend and not simply a purchaser, Dale leaves, and later that night witnesses a murder. Fleeing in a coughing fit of shock and smoke, he drops his joint, containing the titular herb. The murderer, local drug kingpin Ted Jones (Gary Cole), samples the joint and recognizes his own wares, pointing the way directly to Saul and Dale, who now have to find a way to not get murdered.

From here on out things get complicated, and the intrigue-filled plot becomes both somewhat nonsensical and completely beside the point. The movie riffs on all the mainstays of standard-issue action films and appears determined to make any possible situation as ridiculous as possible.

A spirited rant from Jones about how he will murder all of his enemies ends with him tickling his companion. Dale interrogates Saul’s supplier, Red (Danny R. McBride), with a cactus. Most of a set-piece car chase takes place with Saul’s foot through a car window. Summed up, no opportunity is missed to make things sillier, and it helps that everyone looks like they’re having a good time.

Rogen, somewhat confined in a straight-man role, still tosses off choice one-liners throughout. Hanging around and smoking makes a perfect set-up for spirited improvisations, and Rogen particularly shines playing off Franco. McBride makes an increasingly bizarre supporting role something special, and under-recognized comedic talents Craig Robinson and Kevin Corrigan contribute what they can as Jones’ henchmen.

Most impressive of all is Franco, who nails his role and consistently proves to be the most interesting character, wearing an easygoing smile throughout and alternately embodying a concerned four-year-old or a relaxed kitten. Even with a particularly manic conclusion, the strong performances let the film endure without the whole structure falling into a sea of accumulated absurdity.

Still, for fans of the filmmakers, “Pineapple Express” is a slight disappointment. The recent films from the comedic collective that has loosely assembled around producer Judd Apatow, including stand-outs “The 40 Year-Old Virgin,” “Knocked Up” and “Superbad,” were excellent, and “Express” fails to meet their high standards. The rich characters and confident plotting of these films provide a frame for free-wheeling improvisation that sustains laughs and interest, and much of its benefits wind up missing from “Pineapple Express.”

The movie’s steadfast refusal to treat anything remotely seriously makes quite a lot of sense, given the story it tells; but the film loses the special, tenderhearted sincerity that made its kindred projects so successful. “Pineapple Express” gets its material too right, mustering a charming and upbeat sensibility, but not bringing about the sense of purpose to make it all come together.