Darren Aronofsky's radical drug-addiction drama was highly acclaimed and angrily slated when it came out in 2000. Today, this Hubert Selby Jr adaptation is no less contentious.

When Requiem for a Dream debuted 25 years ago in May 2000, it drew both rave reviews and a firestorm of controversy. The midnight screening at the Cannes Film Festival culminated in a rapturous standing ovation from the auditorium's 3,000 spectators. When the lights came up on author Hubert Selby Jr – who had written the 1978 novel on which the film was based – tears were streaming down his face. Critical admiration followed, with the Guardian's Peter Bradshaw rhapsodising that director Darren Aronofsky had reached the legendary heights of Orson Welles in "energy, consistency, and utter mastery of technique".

The reception played out very differently, however, at the Toronto Film Festival, where some audience members vomited in disgust. Saddled with a restrictive NC-17 rating, the film went on to gross a lean $7.5m (£5.5m) on a $4.5m (£3.3m) budget, and was lambasted by some detractors for, as Jay Carr put it in the Boston Globe, "slumming in a vision of hell hatched from bourgeois comfort".

What divided critical reaction was how Requiem for a Dream depicted drug addicts – which is to say, in up-close, harrowing detail. The film follows a widow, Sara Goldfarb (Ellen Burstyn), as she becomes hooked on diet pills in an effort to become a contestant on a television game show. Meanwhile, her son Harry (Jared Leto) and his best friend Tyrone (Marlon Wayans) hatch a scheme to get rich selling heroin. When things go south, they pressure Harry's girlfriend Marion (Jennifer Connelly) to trade sex for drugs. The plot swirls like a whirlpool that draws them toward their gruesome fates: torturous treatments of electroconvulsive shock therapy, amputation of a gangrenous arm, conscription into a prison work gang overseen by a racist guard, and exploitation in humiliating sex work.

The film-makers set out to deliver a sensory bombardment that would mimic the experience of addiction. But they ended up doing much more, touching off serious debates about the free will of the addict, the line between compassionate observation and exploitative voyeurism, and the toxic siren call of the American Dream itself. Twenty-five years later, these debates are still smouldering.

The idea for the film came when producer Eric Watson noticed a copy of Selby's novel sitting on Aronofsky's bookshelf in 1998. "Darren told me he'd had to stop reading halfway through – it was just too dark and unrelenting – and that intrigued me," Watson tells the BBC. "I asked him if I could borrow it for something to read on a ski trip with my parents. It completely ruined my holiday. I told Darren when I got back, 'This is the one – we've got to make this movie'. So we optioned the novel for a thousand bucks, and rather than wait for Selby to find the screenplay that was lost in his attic, Darren wrote one himself."

Aronofsky and Watson sent the script to all the major studios. The response? "Crickets," Watson recalls. "No one even bothered to call us back to turn it down." Undeterred, they secured half the funding they needed from Artisan Entertainment, and brought aboard an independent producer, Palmer West, to help gather the rest of a shoestring budget. The casting process proved challenging, too. "Tobey Maguire, Adrien Brody, Joaquin Phoenix, Giovanni Ribisi – they all explored the project or showed up to audition to be Harry, but turned down the part," Watson recalls. "It was just too much of a career risk."

Once Leto, Connelly, Wayans and Burstyn were cast, the actors strove for authenticity. Leto shed 25lb (11kg)........

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