Photo: MUBI/Courtesy Everett Collection

The substancedirector Coralie Fargeat's new body horror film about the curse of aging in Hollywood is masterfully made. Each image could be installed in a gallery like a work of art. Every cut and sound choice is designed to elicit maximum discomfort in the audience. Everyday noises are blasted into our eardrums at high volume, like reverse ASMR, and there's never a still camera shot when it could have been something falling or from a low perspective or a maximum close-up. As two halves of one self divided by the titular substance, Demi Moore and Margaret Qualley commit to overt, asexual nudity and many varieties of physically and emotionally extreme performance, both actresses at their best. I'm still dazzled by the level of pure spectacle. Still, there's something wrong with the central idea.

Yes, the film clearly uses maximalism and shock effects to convey its message. But the price for enthusiasm The substance is to accept, wholesale, that a woman would be willing to give up her life for seven days to allow a version of her young, beautiful self to strut the world in her place. The two selves share no common mind, so the old me is left to sit around and watch TV while the new me enlivens the town. Why, I wondered, would anyone make that trade? Part of my inability to suppress my skepticism may be because Demi Moore, who plays faded star Elisabeth Sparkle, is one of the most beautiful 62-year-olds on the planet. If you're pretty much perfect, why sacrifice everything to have a radiant Margaret Qualley burst out of your spine every two weeks?

When we first meet Elisabeth, it's done symbolically: We see a montage of her star being carefully installed on the Walk of Fame, shiny at first, then faded and brittle over the years, ignored by the tourists who walk over it and notice it less and less. Then we meet Elisabeth in real life on the set of her long-running aerobics show, where she's sweating in a skintight leotard and tights, looking fantastic. But not fantastic enough for Harvey, played by Dennis Quaid, the studio's boss and avatar of all things masculine and rapacious in Hollywood. In shiny suits and clanking boots, his face contorted in punishing close-up, he loudly chews shrimp for lunch in a way that will never let you eat shrimp again. As he does this, he fires Elisabeth from her show for being too old. She immediately drives out and crashes her shiny red car, distracted from traffic by the sight of her oversized face being peeled off a billboard. At the hospital, she is subsequently declared to have made a safe recovery, but a beaming, youthful doctor's assistant hands her a card with a phone number and the words “The Substance,” wrapped in a note that reads, “It changed my life.”

Alone in her jewel-toned apartment with a mercilessly bright window that overlooks the city the entire wall, Elisabeth smashes the shrines she's erected to her own beauty, then calls the number as we know it. Soon she receives a numbered access card in the mail. As far as we know, no money is exchanged. She is simply given directions to a mysterious, grimy back alley where, at the end of a rubble-strewn corridor, stands a bare, white room filled with lockers. Her locker opens to reveal a cardboard box, innocent as an Amazon package, containing the kit that will poison her future. She doesn't hesitate, not for a moment, before using the kit, which comes packaged with a series of frightening warnings. Of course, our culture's sexism and beauty obsession leaves women desperate for solutions. But… so desperate?

Here's how the substance works: First, in her laboratory-like white-tiled bathroom, under harsh lights, Elisabeth must strip herself to the point of nudity and examine her aging body. I must reiterate that she looks great, slim and lithe, with preternaturally perky breasts and an ever-so-slightly saggy bottom. Then she must inject herself with a vial of a greenish liquid, then writhe on the floor and moan as the liquid takes effect. Her greenish pupils split in half and blue twins sprout to populate her eye sockets. A horrific knot distorts the flesh of her back. Then Margaret Qualley's character Sue emerges from a clear line running down her spine. Sue is then tasked with sewing up the hole she emerged from with knots of thick black thread, in a scene that elicited audible groans from the audience I saw the film with. We hear the needle sting and slide as it penetrates a thick lump of skin. The procedure is completed with the insertion of an IV bag of nutrients labeled “NUTRITION” (an identical bag is labeled “NUTRITION: OTHER SELF”), and Elisabeth's half-alive sack of flesh is left in a puddle of yellow and pink juices on the bathroom floor to wait out the next week. Oh, one more thing! To avoid getting dizzy and suddenly getting a nosebleed, every day Sue must insert a large hypodermic needle into Elisabeth's exposed spine and withdraw a clear fluid, which she then injects into her own flank, Ozempic-style. This must be done for seven days in a row, after which the selves must be switched without fail, according to the instructions included with Elisabeth's first substance kit.

Sue immediately sets out to take Elisabeth's old job. Everything goes smoothly – the TV audience loves her! She twirls around under relentless lights in a shimmering pink leotard with cutouts, smiling wildly at the camera. As Elisabeth enters her final week in the world, things look a little grimmer. She heads down the trash-strewn alley to get more tubes and IVs. After meeting a high school acquaintance who remembers her as the prettiest girl in the world, she takes his number even though he's completely unattractive and arranges to meet him later. As she gets ready to go out, she turns back to fix her outfit and apply more and more makeup, becoming increasingly dissatisfied with what she sees in the mirror. Finally, in a gesture of wild disgust, she applies a line of lipstick to her cheek. It's one of the film's hardest scenes to watch; she seems to be literally about to rip her face off.

The problem is that as I watched Demi Moore rub more and more concealer and blusher into her unnaturally smooth cheeks, I couldn't help but think about how amazing she looked. Even when she gave up on the date and collapsed, she still looked, if not 26 and radiant like her other self, but like a beautiful movie star who has had expensive and elaborate facial procedures done to make her look at least ten years younger than her actual age. Who wouldn't want that? The substance depends on the audience assuming that nothing but a perfect, perky butt and smooth limbs is an acceptable look for any woman, but a few more visible wrinkles or lines on the neck would have sold the premise much better.

When Sue inevitably oversteps the bounds of the one-week rule and takes a few hours more than she was allowed, the consequences are evident in Elisabeth's body. First, Elisabeth grows a monstrous, withered, bony finger with a long, opaque nail. It looks conspicuously out of place on her otherwise magnificent body. What if the change had instead been more superficial? A few strands of gray hair, a hint of belly, a handful of forehead wrinkles that gradually develop as Sue steals more and more of Elisabeth's being? Instead, the film goes all out. Sue drains Elisabeth's body of every last remnant, stopping only when her spinal fluid has completely dried up. Then she is forced to switch places or, it is implied, die. Of course, this happens at the worst possible moment: she has just dragged a hot biker into her apartment for sex. The nightmarish version of Elisabeth coming out of the bathroom and chasing the man out of the apartment – with a hunched back and bursting varicose veins – is good for laughs and scares, but what exactly does this transformation mean?

The progressive decline of Sue and Elisabeth in the final third of the film is a sustained experience of maximum grotesqueness, the performance and craftsmanship of which I admired. Battles are drawn and the gleaming apartment is trashed in various hilarious ways. At one point, the old Elisabeth leaves the apartment full of dishes she cooked from a classic French cookbook, leaving them to rot everywhere. The end of Sue's attempt to appear on her TV station's New Year's Eve show shall not be given away, but I should mention that gallons of blood are splattered. It's hard to imagine a harsher punishment for wanting to unleash a younger self on the world.

My absurd wish for this decidedly unsubtle film was simply that it had lightened its relentlessness with more moments of precision. What a thoroughly terrifying—because familiar—moment it would have been if Elisabeth had noticed a small change in her flawless appearance, a stray, unruly gray chin hair, or the shock of a prominent vein on an otherwise smooth thigh? The natural process of aging is gross, this film seems to say, and of course audiences agree. But taking this cultural dictate to its most outlandish extremes seems ultimately superfluous when the truth is horrific enough.