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“Vanity of vanities; all is vanity,” says the Good Book, and “The Substance” hastens to add a few more ingredients to the condemned’s last meal: fears of aging, sins of the flesh, daytime exercise shows, the monstrous egotism of Hollywood stars, and buckets – no, tsunamis – of blood. And Demi Moore, fearlessly and hilariously biting the hand of the entertainment industry that made her.

The second feature written and directed by the nervy French filmmaker Coralie Fargeat (“Revenge”) is most definitely not for the faint of heart, but if you like your moral fables served up with a liberating lack of restraint, here’s your movie – a cautionary tale that suggests an EC horror-comic version of a “Twilight Zone” retelling of “Sunset Boulevard.” “The Substance” starts as a drama, but by the final act, it’s become a gory gonzo comedy – the logical end point of Botox Nation.

Moore plays Elisabeth Sparkle, an Oscar-winning, A-list actress whose star on Hollywood Boulevard we see tarnish into time-lapse neglect over the years in the film’s neatly metaphorical opening sequence. By the time “The Substance” properly begins, Elisabeth is hosting a Jane Fonda-style workout show and is holding on to that job by a thread, since her boss – a braying, misogynistic Dennis Quaid – wants to jettison her for a newer model.

How desperate is Elisabeth to reverse her fortunes and the erosions of time? Enough to sign up for a mysterious rejuvenating regimen called the Substance without bothering to read the small print. The stuff promises “a new you,” and that’s what Elisabeth gets: a bloodily birthed clone of her younger self, renamed “Sue” – just Sue – and played by a vampy, vacant-eyed Margaret Qualley.

The catch? Each Elisabeth is allowed a week out in the world before having to switch places and recharge for a week, a schedule that eventually creates professional jealousy, a severe case of split personality and a decision to no longer follow the rules.

You know what happens in these movies when you don’t follow the rules.

“The Substance” doesn’t just court vulgarity, it gleefully rolls around in it. The movie shows us Elisabeth’s sagging body through the character’s own self-loathing eyes, and it pushes the camera into Sue’s breasts and butt as she flaunts her stuff for Quaid’s network boss, whose eyeballs practically bounce around on springs like a cartoon wolf’s. Fargeat goes heavy on the fish-eye lenses and long, Kubrickian corridors; “The Substance” bludgeons a viewer with style well before the characters start bludgeoning each other.

Ironically, what saves the movie is its own excess. At a certain point – around the time Elisabeth’s canyon-top mansion gets trashed in a melee and one final plot twist ups the gross-out factor by a factor of 10 – “The Substance” stands revealed as a splattery farce, in which literal geysers of blood coat the walls and our culture’s worship of the body young and beautiful is given a high-spirited thrashing.

And the star? For an actor who has never shown much of a sense of humor about herself, Moore is remarkably and absolutely in on the joke. And why not? As a 61-year-old woman in an industry run by vain old men, she’s lived it. If it’s mildly distressing to see an actress of Qualley’s smarts play an avaricious bimbo – she stoops to conquer – Moore more than makes up for it with her total commitment to Elisabeth’s toxic insecurity, a need to be seen, and seen as forever young, that’s as much an indictment of the culture that elevated her as the self-absorption that blinds her.

With wit, style and ruthlessness, Fargeat has made a movie that’s an example of the soulless pop-culture object she’s spoofing. That’s asking a lot of some viewers, but others will be willing to follow Elisabeth and Sue far past the point of no return. “The Substance” cheekily suggests that the celebrities we adore will inevitably turn into the monsters we deserve.

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Ty Burr is the author of the movie recommendation newsletter Ty Burr’s Watch List at tyburrswatchlist.com.

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Three stars. Rated R. At theatres. Contains strong bloody violent content, gore, graphic nudity and language. 140 minutes.

Rating guide: Four stars masterpiece, three stars very good, two stars OK, one star poor, no stars waste of time.