The concerned citizens file onto the stage: 12 adult actors dressed as well-to-do parents and respectable high school students. One couple is holding hands. A girl wears the sash of a prom queen. A boy holds a football — he must be the quarterback. Sitting in their chairs upstage, they’re nervous, proper, all-American.

The Lecturer, played with grim world-weariness by Jody O’Neil, approaches the podium downstage and addresses the audience directly. He’s here to inform us — we’ve been cast as concerned citizens, too — about the “leafy green assassin” that is destroying the youth of America in increasing numbers. Tonight, he proclaims, at Benjamin Harrison High School, the rosy-cheeked, bright-eyed cast of the school’s production of Green Grow the Lilacs will assume roles for a darker production: they’ll re-enact the “true events” that exemplify the danger of “public enemy number one”: marijuana.

The performance of Reefer Madness at the Wellfleet Harbor Actors Theater has only just begun, and the audience is already laughing. The show, written by Kevin Murphy and Dan Studney, premiered in Los Angeles in 1998; it’s a musical satire of the 1936 film of the same name, which terrorized impressionable parents at the time.

The original propaganda film, directed by Louis J. Gasnier, in which the actors employ thick Mid-Atlantic accents, now seems comical. Originally titled Tell Your Children, it features high school and college students hooked on dope and committing violent crimes from attempted rape to murder. The wild hallucinations and depravity on parade in the movie seem particularly suited to a remake as a musical — a genre that lends itself to absurdity.

Like the movie, the musical strings together a series of peril-ridden vignettes that tell the tale of the Harper Affair, a terrible scandal, says the Lecturer. So ensues a reenactment in which young Jimmy Harper (Kyle Becker) falls in love with Mary Lane (Maranda Rossi). In confident voices — Becker projects with ease, and Rossi’s got stunning clarity on the highest notes — they sing of love as they study Shakespeare on a picnic blanket. When they kiss, Mary Lane kicks a leg into the air. It’s all an innocent caprice.

Harper visits the local five and dime, where the cast swing-dances bouncy-fun choreography by Constantine Baecher, led by sure-footed dance captain Madison Troost.

But then, alas, Harper is lured away by Jack (Brian Lore Evans), the local dope dealer, pimped out in a boxy suit, who promises dance lessons and instead takes kids to his “reefer den” — the room behind the curtain.

Scenes set in front of the curtain are sparsely equipped with props: a steering wheel, a blanket, an electric chair. The reefer den has ragged couches, a messy table, a long-suffering plant, and characters who are as purposefully contrived as those in the original film. Ralph (Gabriel Graetz), a bearded “college boy” turned maniacal pot addict, keeps company there with two sultry, loose-limbed women, Sally (Paige O’Connor) and Mae (Brittany Rolfs), who are draped over the furniture in weed-induced stupors.

Mae doesn’t approve of Jack’s bringing home kids. She’d prefer to stick with adults. But she’s desperate for “the stuff,” and she must appease Jack to get it. Rolfs’s Act I performance of “The Stuff” is one of the most memorable of the show. Her portrayal of the jaded, melodramatic Mae is addictively, hammily tragic.

The 13-person cast has Reefer Madness’s 18 characters down. As teenagers, they dance and giggle with abandon. Brian Lore Evans plays Jesus in more than one scene, to the audience’s cackling delight. He wiggles a flamboyantly disapproving finger at Harper, saying, “Take a hit of God instead. Do you think you can handle the high?” But his power is half-baked, evoking the low-budget quality of the original film. The shoddy wreath on his head is lopsided; we can see his pants and dress shoes poking out from beneath his saggy robe. Graetz plays “Sally’s Baby,” with pink dots of rouge on his cheeks, as convincingly as he plays Ralph.

O’Neil, self-serious as the Lecturer, returns ably as several different characters, each walking with a different gait and staring with a different gaze: the resigned man behind the counter at the five and dime, an investigating police officer, a deity of chaos crowned with marijuana leaves and grapes, and in the end, President Franklin D. Roosevelt in a wheelchair.

The band, hidden behind the stage, plays so precisely you might confuse its sound for recorded tracks. But there’s no mistaking the energy of live musicians, led on opening night by conductor Matthew Stern, who never missed a cue. A jazzy refrain that accompanies the words “reefer madness” and, later, “eat the brownie” is just one of the ways the music makes the story memorable. All of the songs, with lyrics by Dan Studney and music by Kevin Murphy, are the kind that leave the audience humming on the way out.

The improbability of the musical’s tragedies is the basis for its comedy. We learn from giant placards held up at intervals by the Placard Girl (Gracie O’Leary), a prim young lady with stern red lips, that reefer will get you raped, and you won’t care; reefer makes you a pathological liar; reefer gives you a potty mouth; it gives you the munchies — for human flesh; it makes you sell your babies for drug money; it annihilates true love and kills poor old men.

In the end, we’re reminded by our American idols, Uncle Sam, Lady Liberty, and George Washington, to save our children. “I want you,” says Uncle Sam, “to drop that joint!” But not only that. In a startlingly relevant final song, “The Truth,” the characters come together on a future plan: to “burn or ban” other things that scare them.

“Once the reefer has been destroyed,” they sing, “We’ll start on Darwin and Sigmund Freud/ And sex depicted on celluloid/ And communists and queens/ When danger’s near, exploit their fear/ The end will justify the means!”

This dusted off Reefer Madness turns out to be a timely show, and in the capable hands of WHAT, also a medical-grade escape into laughter.

Comedy is an indispensable tool for confronting the incomprehensible and also for processing frustration and anger. At intermission, the voice of one audience member rose over the gabbing: “I haven’t smoked pot in a long time, but this show is making me think I should try it again.”