Small-screen actor Zach Braff makes his big-screen debut as director-writer-actor of the award-winning comedy Garden State. Anna Carey talks to the Scrubs star about capturing the life of a real twenty-something

The most striking thing about comic-actor-turned-acclaimed director Zach Braff is that, unlike many famous people, he is much taller in real life than he looks on TV. The second most striking thing about Zach Braff is that, when we meet at noon in a Covent Garden hotel, he is very, very tired.

And hungry. Braff has just jetted in to London, he's done four interviews already this morning, and he still hasn't eaten anything. He's been talking about his debut film, Garden State (which he wrote, directed and stars in) for weeks now. Frankly, he's a bit knackered.

Luckily, Braff is unfailingly polite and friendly, even when stifling a sleepy yawn. Maybe it's because he knows that his breakfast is going to arrive in a minute.

The 29 year old, who has been acting professionally since his teens, is best known for his role as the likeably goofy doctor John "JD" Dorian in the excellent medical sitcom Scrubs. But he always wanted to work behind the camera. "I made movies all the time as a kid, and I always dreamed of being a film-maker," he says.

Braff studied film-making at prestigious Northwestern University in Chicago. Although he concentrated on acting after leaving college, he knew he still wanted to make films himself. But did he always want to do an Orson Welles and write, direct and star?

"Well, I always knew I wanted to both write and direct something. I wasn't positive that I'd actually play the lead in it. But as we got further along [ with Garden State] I just decided that, as an actor, this part was an enormous break which I could give to myself! If I hadn't written this film I probably wouldn't even have got an audition for it."

In fact, it's rather surprising that he was allowed direct it, too. Braff's film-making experience prior to Garden State had consisted of a few well-received but little-seen shorts. "I think I just projected confidence, even when I wasn't confident at all," he says. "And also, I think a lot of people in Hollywood really do think that the best person to direct a film is the person who wrote it. People [ in production] were very supportive. Maybe they just knew that I wasn't going to relinquish the direction of it to anyone!"

It's hard to imagine anyone else doing a better job. Beautifully shot and superbly acted, Garden State is a remarkable debut by anyone's standards. Braff plays Andrew "Large" Largeman, a struggling actor who returns to his native New Jersey from LA to attend his mother's funeral. He hangs out with his old schoolfriends, tries to connect with his father, falls in love with a sweetly eccentric girl. And he stops taking the anti-depressant drugs that he's been on since he was a child.

It's a charming, sad, funny and strange film, with an excellent cast: Ian Holm plays Large's father, Natalie Portman his love interest and Peter Sarsgaard his former best friend.

"I got all the actors I wanted straight away," says Braff. "They were all my first choices - I didn't expect them all to say yes, but they really responded to the script." In an unlikely piece of casting, Method Man from the Wu-Tang Clan also appears in a memorable cameo. "Method Man and Ian Holm together at last," laughs Braff. "But he's actually a really good actor."

Garden State is a love story, but it's also a coming-of-age film, one which asks the question faced by everyone when they're growing up: what, and where, is home?

"I think that a big part of your twenties is figuring out what home is. If home is no longer the house where you grew up, and you don't consider the little apartment where you live with no money to be home, then what does the concept of home mean?

"I mean, when I went to college [ in Chicago] I was incredibly homesick, but at the same time I didn't feel like my parents' house was my home anymore. So I remember feeling homesick for a place that didn't really exist. I think - and I wanted to get this across in the movie - that when you grow up the onus is on you to create a new home for yourself. You need to be strong enough to do that."

It's a fact of twenty-something life which is never usually seen on film or TV, where characters are often unrealistically secure. "I feel like there are so many films which are marketed as twenty-somethings, but very few which are actually about being twenty-something," says Braff. "All I could do was write what I knew. And I knew ... well, what you saw on screen in the movie."

But what Braff knew seemed to strike a chord with many of his peers. For a film with relatively small distribution, Garden State has been phenomenally successful, with fans apparently returning to the cinema for multiple viewings. "I didn't know that so many people would respond to it," he says. "I thought well, there are going to be a few people out there who like this sort of movie, who are interested in something truthful and personal. But I had no idea it would get the sort of reaction it got."

When the film was released in the US, Braff started writing a blog on its website, which quickly attracted a devoted following. Glancing at the readers' comments on the site gives an idea of how much people really, really like this film.

"It's like a cult!" says Braff, in a charmingly JD-ish way. "They call themselves FOGS - Friends of Garden State. I think there are a lot of people who have felt these feelings and haven't ever had anyone say 'me too'. So maybe this movie allows people who are lonesome or depressed or confused - not necessarily people in their twenties - to realise that other people are going through this, that it's okay."

Fans also responded to the film's soundtrack, which made a cult hit out of the song featured in the trailer (Let Go by Frou Frou). Braff put the soundtrack together himself and won a Grammy Award for it. "I actually made a mix CD when I gave out the scripts to everyone and said this is the music I want to put in the movie. And most of that mix CD ended up in the movie. I didn't think we'd get the rights to everything, like Simon & Garfunkel, but even when people said no we'd show them the movie and then they said yes. It was amazing. The only person who still said no was Fiona Apple."

The film is not, Braff stresses, an autobiographical work, but there are certainly autobiographical elements. Like Large, Braff was a struggling actor for some time after college. At the start of the movie, Large is working as a waiter even though he's just starred in a major movie. This is based closely on Braff's own early experiences. "I was in this film called The Broken Hearts Club, which was playing round the corner from the restaurant where I was working in LA," he says. "And people would come in to eat after the movie and I'd be there waiting on them. They'd be like, 'wow, you were in that movie, you were really good!' And I'd be all, 'Thanks. Let me tell you about our specials... '"

And, like Large, who we discover is best known for one starring role as a mentally handicapped football player (Natalie Portman's character is surprised to find out that he's not actually mentally handicapped himself), Braff played his share of roles that proved embarrassing when he came home.

"The most embarrassing thing I had done was, of course, the only thing everybody at home had seen," he says. "It was a [ 1994 TV movie] where I was in full drag. It was kind of like Tootsie: in order to get the girl I had to dress up as a girl, and then I learned lessons about how hard it is to be a woman. And it seemed like literally everyone I'd ever known in New Jersey saw that one."

A starring role in Scrubs, which premiered in 2001, allowed Braff to put on-screen transvestitism behind him forever, and gave his old neighbours something a little less cringeworthy to talk about.

"It totally transformed my life. I mean, it's basically given me a career. You know, I was a waiter, and now I'm sitting here talking to you about my film. And this wouldn't be possible without Scrubs."

He's obviously a genuine fan of the show in which he stars. "It just makes me laugh," he says. "Very little TV makes me laugh, but this does. And the characters are great."

He's particularly fond of JD's magnificent nemesis, the nameless hospital Janitor, and says that the cunning custodian's name will never be revealed. "Never. I don't think he actually has a name. The characters have just started calling him 'Janitor' in the show, especially Sarah [ Chalke, who plays Eliot], which is just... " He shakes his head, laughing uncontrollably.

Braff recently directed a few episodes of the sitcom. "It's weird directing your friends, but everyone was very supportive," he says. "I'd definitely do it again." But he admits that directing Scrubs is very different from directing his own project.

Despite the critical and commercial success of Garden State, Braff has no plans to leave Scrubs, but he's also sticking with film-making. His next project is an adaptation of a children's book called Andrew Henry's Meadow. He's currently working on the script with his brother Joshua, himself a novelist.

"It's a book I loved as a kid, and I think it would make a cool kids' movie," he says. "What's it about? Well, it's hard to describe, but basically it's like if Terry Gilliam directed The Goonies."

It sounds like quite a challenge. But then, having battled with Janitor, appeared in drag in front of all his old neighbours, and written and directed his own film, Zach Braff shouldn't have too much of a problem with that.

Garden State opens on April 8th