The rapper Jay-Z heralded the band as “a movement”, and took his girlfriend, Beyonc?nowles, to a New York show last year. The first album they made together, Fall Out Boy’s Evening Out With Your Girlfriend, was released by the California indie label Uprising. They were then signed by John Janick, co-owner of the Florida indie label Fueled by Ramen, and the band released their first full-length album, Take This to Your Grave in 2003, inspired by Wentz’s break-up with his girlfriend (who has since become famous in her own right for her presence in the album’s lyrics) Island Records snapped them up later that year. They had all been involved in Chicago’s hardcore scene, playing in a handful of bands, when they met. The problem is I can get addicted to that feeling that you get from writing a song that can get unhealthy because you are relying on it.” He does therapy even when he is on tour “It helps just to be able to give what you are thinking out Keeping it in your own head is not always the best thing.

When I’m home I do it most days, but when I’m on the road I do it on the phone.” The band – all from Chicago – formed in 2001, taking their name from Bart Simpson’s favourite superhero, Radioactive Man’s sidekick. He says the depression wasn’t caused by any particular trauma in his childhood, which was “pretty mundane – the mundane and the ordinary can be very depressing Very, very depressing,” he says “I find that writing songs is cathartic. He has admitted to a fascination with the suicides of Elliott Smith and Joy Division’s Ian Curtis. But there is nothing fake about this dark period of his life, just stark honesty. Mom’s [a school administrator] in the kitchen baking stuff, and dad’s [a lawyer] off at work. It’s very non-exceptional.” Wentz says that sleeping in the bedroom that he grew up in made him “more sensitive to adolescent angst”. He withdrew from the rest of the band, only appearing to hand them his lyrics.

But after the near-death episode – he had his stomach pumped – Wentz moved back into his parents’ house in the posh Chicago suburb of Wilmette (“A place straight out of one of those Eighties movies like The Breakfast Club,” he says), leaving the rest of the band to tour the UK in February 2005 without him “It’s really boring there Not a whole lot going on. I was racked with self-doubt.” He had been obsessed for a while with the tsunami and his own mortality. It is particularly overwhelming when you are on the cusp of doing something very big and thinking that it will be a big flop. I didn’t really think about whether I slept or died.” About this dark time in his life, he says: “It was overwhelming I was either totally anxious or totally depressed. In the Best Buy parking lot in Chicago, full of pain – “my head was racing with self doubt and negative thoughts” – he swallowed a handful of Ativan anxiety pills in an act that he calls “hypermedicating” He recalls: “I just wanted to have my head shut up. “In an age when people can so easily click a button and download it’s not good enough to just give somebody a song,” says Wentz.

Suffering from depression – “black clouds” – he has described his moods as “oil and water and they never mix together right”. In February last year, just as the band were recording their breakthrough album, Wentz went into emotional meltdown. “It’s a bit like [Nikolai Gogol's] Diary Of a Madman,” Wentz says. “My inspiration and my ideas don’t begin and end at the beginning and the ending of a song. It is too limiting.” It is no wonder that the singer, Stump, said of Wentz: “It scares me sometimes, watching him. The two seconds you’re not with that dude he’s made 30 decisions that are going to affect us for the rest of the year.” Then there is the band’s MySpace page, buzzing with more than 750,000 ” friends” living in the band’s online, virtual community.