Bradley Cooper: boy to man

If you interview Bradley Cooper in Los Angeles, it tends to go something like this: actor picks up journalist at around 6.30am in running gear, drives out to Hollywood Hills with dog in back of car, takes run along Malibu beach. Then it's back to his for breakfast, softening up said journalist with an omelette.

The London version is more prosaic. Preparing for the premiere of his new film Limitless, Cooper flops down on a sofa in his hotel suite, feet up on the coffee table, midriff exposed (I don't think he notices). Berocca vitamin drink in hand, he lets out an easy drawl: "What about this room? Jesus Christ, this room is so opulent. It's ridiculous." Which is true: a garishly twee oil painting of cute birds hangs behind him.

Cooper is not a household name, not yet anyway. His effortless performances as a badass in both Wedding Crashers and The Hangover may have catapulted him into Hollywood's big league, but what hasn't been so easy, he says, is getting the industry to see past all that off-the-leash, bad-taste humour. "People go, 'Isn't he just the guy from The Hangover?'" Which is fine up to a point because, despite featuring no big-name stars, The Hangover was massive, the highest-grossing R-rated comedy ever – a story of three guys on a stag weekend in Vegas who wake up sans groom, with a tiger in the bathroom, a baby in the wardrobe, and Jägermeister-and-Rophenol hangovers.

At 36, Cooper must know that he can't play man-boys for ever. Moreover, unlike his funny co-stars (Zach Galifianakis, Ed Helms et al), he never set out to be a comic actor: until recently, he says, he took whatever work was offered. The new film Limitless, in which he appears alongside his acting hero Robert De Niro, is his meatiest role yet: a chance to prove he has got more going for him than locker-room good looks. Does he feel like his leading-man mettle is being put to the test? "Yeah, well, we'll see. This is an opportunity to prove that."

You might have seen some of the posters for Limitless: a rip-off of vitamin supplement ads, they offer the grandiose promise of "the perfect version of you". There's a shot of Cooper looking tanned and goal-achieving alongside a list of side effects: psychosis, homicidal blackouts, sudden death, etc. Nowhere is the movie mentioned – this poster is daring you to be interested enough to look up the website.

Cooper plays a writer who's been chewing on his debut novel for a decade, going nowhere until he bumps into an old drug-dealing buddy who gives him an unlicensed super-pill, NZT. The plot is a play on the specious statistic that we only use 10% of our brains ("Anyone who believes that probably is," says one psychiatrist). Taking NZT, this no-hoper becomes unstoppable: he can recall everything he's ever read; he finishes writing a genius novel in four days; he learns French in an après-midi. Even his misspent hours watching Bruce Lee twirling nunchucks are put to use when Russian mobsters come after his stash. He makes a fortune on Wall Street, becoming the protege of uber-billionaire De Niro (who, inexplicably, is called Van Loon). There are side effects, of course, and by the end the whole thing has a very 1980s American Psycho cocaine paranoia to it.

The premise is irresistible: don't we all secretly believe that we've got some buried-away genius waiting to be unleashed? Equally pleasing is the thought that some shadowy Bilderberg-style group is necking pharmaceuticals to stay on top. Ah-ha, so that explains Mark Zuckerberg's savant genius. "Or Bill Gates, Richard Branson, Steve Jobs," chirps Cooper. He takes his feet off the coffee table, crosses his arms and pulls a stern face: "Then you've got Rupert Murdoch who is going, 'Where did all these guys come from?'" Limitless will not disappoint Cooper's man-fans (and there are plenty of them). Like the guy-comedies that have made him so bankable, and whose charm lies in their sweary but ultimately unrisky wholesomeness, all the hard work goes on beneath a jock-ish, jokey surface.

Cooper has been dating Renée Zellweger. So what's the most scurrilous thing he has read about himself? "Scurrilous, what's that? Like scandalous? I never heard that. How do you spell it? S-c-u-r-r . . . ?" Cooper is good with deflective shots like that – the day after we meet, gossip mags report that they have split. Does he have a hard time with paparazzi? No, it doesn't bother him. "The only thing that's different now is that my mother lives with me, and she didn't ask for it all." At the end of last year, Cooper moved back in with his parents Gloria and Charles for four months to be close to his dad, who died of lung cancer in January. His mum has been travelling with him ever since. "Except to here. She's back in Philly. But I'm Italian, so that's just the way it is."

He grew up Philadelphia, the only blond-haired kid in an extended family of Italians, meaning everyone thought he was a girl. His mum is Italian-American, his dad Irish-American, and no one from his family had ever acted. "The idea I was going to be an actor scared the shit out of my parents. My dad was the first one to go to college in his neighbourhood. He built a nice life. He was a stockbroker – and then his son wants to be an actor?" Cooper senior was, however, a film buff, and his 12-year-old son got the acting bug after watching John Hurt in David Lynch's The Elephant Man.

Is the demi-mane a hindrance?

Cooper took a degree in English before moving to New York to study acting, making his first TV appearance before graduation, in an early episode of Sex and the City as one of Sarah Jessica Parker's squeezes. "No tongues," he was told. You do wonder if the piercing blue eyes and demi-mane of blond hair have hindered him when it comes to being taken seriously. The question provokes a burst of guffawing. "That's bullshit. I can tell by the way you're asking, you know it's not true." No one has ever told him he is too good-looking for a role. Ever. "In fact, I've always fallen between the cracks of not being good-looking enough for certain roles and not odd-looking enough for other roles." Which can't be entirely true, since he was cast as lover-boy Faceman in last year's A-Team remake.

Back in 2005, though, it was Wedding Crashers and his locker-room-aggressive character Sack Lodge that got Cooper his Hollywood breakthrough. "I loved playing that role. It was the first major movie I'd been part of it. I was acting with Vince Vaughn, Owen Wilson and Christopher Walken." He backslaps the sofa. "It was insane. And I get to play the heavy." Equally alpha but less sociopathic was Phil, ringmaster of bachelor-party bacchanalia in The Hangover. Both roles added another dimension to his screen presence, a kind of wry knowingness: yes, the camera loves me; yes, women love me; yes, men love me; yes, I'm an asshole; yes, so what?

Phil in The Hangover, he says, was his hardest role. "That guy is so different from me. I'm always amazed by it, actually. When I look at that character on screen, I don't see me at all." He admits a lot is riding on Limitless. "This movie is dependent upon me much more solely to tell the story. So if it's successful, hopefully more people will allow me the opportunity to tell that kind of story. You know what I mean?"

He has not long finished filming The Hangover Part II, reportedly for a fee of $5m; he's keen to point out it's not a no-brainer sequel. "This was not a knee-jerk reaction. We met many times to discuss the script. And it was the hardest movie I've ever done." How? "It was like Apocalypse Now: the Comedy. They could make a documentary – like Hearts of Darkness by Coppola's wife – about it." Hangover 2 is set in Bangkok, a city famous for its cultural landmarks as well as for sleaze and sex tourism. He won't go into details, but it doesn't take a genius on a miracle pill to guess what side of the city the overgrown frat-boys will be lured into.