As he demonstrated with his art-house success, the inventive "Pi," writer-director Darren Aronofsky isn't afraid to take chances. For his second work, Aronofsky delivers a knockout punch with the heavyweight drama "Requiem for a Dream." To label this latest film a mere cautionary tale about drug addiction doesn't say nearly enough about its unnerving reality or its staying power. Though dark and disturbing, "Requiem" never ceases to be absorbing. Like witnesses to a tragic accident, moviegoers will find themselves unable to look away. Let me also add that while "Requiem" may be one of the most uncompromising anti-drug stories committed to film, it is not for everyone. In fact, because of Aronofsky's dedication to making sure the movie pulled no cinematic, sanitized punches, the film originally received the dreaded NC-17 rating from the MPAA. Refusing to sacrifice art to commercialism, Artisan Entertainment and Aronofsky decided to release the film unrated. As with "Pi," "Requiem" starts off slowly, deliberately. As we're introduced to each of the characters, Aronofsky uses a split screen to show how each is connected to the others. Visually, we see that the central character is Harry (Jared Leto), a young man just getting by because everything he earns, saves or steals immediately gets turned into something he can inject into his veins. His best friend and partner, Tyrone (Marlon Wayans), has aspirations similar to Harry's, but also as with Harry, Tyrone's hopes and dreams are shattered by drug addiction. The third character in this drama is Marion (Jennifer Connelly), who not only is Harry's girlfriend but also an addict. Finally, there's Harry's widowed mother, Sara (Ellen Burstyn), also an addict, though her drug of choice is television. The story picks up momentum when Sara learns that a marketing company may be able to offer her a spot in the studio audience of a live TV broadcast. "I'm somebody now, Harry," she declares. To make the most of this once-in-a-lifetime opportunity, Sara decides to lose 30 pounds so she can fit into old dress. Her "nice" doctor willingly prescribes the pills to help her do that, choosing to ignore Sara's scarier symptoms. Sara soon becomes just like Harry, Marion and Tyrone, the drugs gradually replacing everything else in life — food, sex, dreams, even the impulse to live. As he draws us into this core group of four, Aronofsky's camera and dialogue always seems to be challenging the audience. He presents us with scene after scene that has us marveling at the degrading depths addicts slip into without a second thought when the promise of a fix is nearby. Aronofsky also has us wondering whether these characters would ever be friends were it not for the shared celebration of the needle. Aronofsky unflinchingly captures the seductive and destructive nature of addiction, leaving us astounded witnesses to the horror and the pity. Much of "Requiem's" power comes from the actors, who deliver performances worthy of accolades. There is not a hint of ego among them as they take their characters down the frightening and degrading rabbit-hole of addiction. Leto and Connelly, both known perhaps more for their physical attributes or their attractiveness than any real depth of talent, here belie those shallow dismissals. Even Wayans, who usually plays the goofy buffoon, here plays it straight and does so with great effect. Burstyn, who usually delivers a strong performance, reiterates her talent as Sara. Though she's certifiable and laughable, Burstyn keeps Sara engaging, making us care for her more than pity her. Aronofsky's trippy style of filmmaking is perfect for the scenes in which the characters are running solely on the juice they've injected. As with the scene where a "speeding" Sara thinks she's being attacked by her fridge, Aronofsky captures both the dark humor of the scene and the shocking truth. Commendably, Aronofsky doesn't sacrifice his actors to the hallucinatory effects he creates. We may be seeing the world through their drug-induced paranoia, but we are always aware of the sad reality. Only during the final stretch, when it becomes obvious just how relentless Aronofsky means to be, does "Requiem for a Dream" teeter on the edge of preachiness. Unflinching and unrelenting, "Requiem" is not a film that will have you shouting from the rooftops about how much you enjoyed it. This is not a movie to enjoy. This is a movie to experience.