The real Slim Shady stands up the fans on his European tour

The US rapper said yesterday that he was cancelling his "Anger Management" tour, due to run from 1 to 17 September, including four dates in Britain and Ireland. A statement on his website said: "Eminem is currently being treated for exhaustion, complicated by other medical issues."

The Detroit rapper, whose real name is Marshall Mathers, was due to appear at the Milton Keynes Bowl, Edinburgh's Murrayfield Stadium and the Lancashire Cricket Ground in Manchester. He was to conclude the tour in Ireland, at Slane Castle in Co Meath, alongside his rap protégés D12 and 50 Cent. The 80,000 tickets for Slane Castle sold out in less than two hours when they went on sale on 10 June.

While still one of the best-selling artists on the planet, Eminem is no longer surrounded by theexcitement of five years ago when he released The Marshall Mathers LP. Insiders have suggested this is as much down to Eminem's own desire to diversify into music producing and other projects including his film 8 Mile, as the changing fashions of the music industry.

His last album, Encore, went to No 1 across the world, selling 11m copies globally, including 1.2m copies in the UK.

It still has a long way to go, however, before matching the success of the The Marshall Mathers LP, featuring the hit singles "Stan" and "The Real Slim Shady", which has sold more than 19m copies worldwide and 2.2m copies in the UK. The Eminem Show, released in 2002, sold more than 19m copies worldwide.

Hattie Collins, editor of urban music magazine RWD, said: "If you look at record sales of the last album it's clear they are declining and his popularity is not what it was. That's kind of inevitable in hip hop - most rappers struggle to go past four or five albums. I see him going into production and just doing the odd guest spot on a track, causing a commotion when he does.

"Hip hop tends to be a young person's game with people looking to who is hottest and freshest."

Gennaro Castaldo, head of press at HMV, said: "It's fair to say Eminem's profile is not quite at the same peak as The Marshall Mathers LP, although he arguably remains the number one male recording artist in the world. This may be partly due to Eminem devoting more time to other aspects of his career."

A spokesman for Polydor Records, which represents Eminem in the UK, said: "Eminem is the hottest artist in the world. There is no one else who is more talked about or selling as many records as Eminem."

The rapper Proof, Eminem's right-hand man onstage, recently said: "Em has definitely gotten to the level where he feels like he's accomplished everything he can accomplish in rap. He wants to kick back and get into the producing thing."

If Mathers is preparing to jettison his Eminem persona in favour of producing, he would be following in the footsteps of his mentor, Dr Dre, a former rapper with NWA who abandoned the mike in his 30s for a successful career as a producer.

Lord Mountcharles, the owner of Slane Castle, said he was stunned by Eminem's pull-out at such short notice. "In all the years that Slane has been running we've never been confronted by a scenario like this. I don't think the Rolling Stones or U2 would cancel a section owing to nervous exhaustion.

"I'm very taken aback. I'm trying to be judicious with my words. I'm not very happy about what has happened. I don't deem that I've had a proper explanation."

He said it was strange that the record company issued a statement without informing him.