Last year, the Dandy Warhols - the kind of rockers who are critically respected but accustomed to being bridesmaids rather than brides - suddenly found themselves fairly famous. A documentary called Dig!, in which they starred, won a Grand Jury Prize at the Sundance film festival, and finally, after a decade, Americans beyond the band's modest fanbase knew who they were.

And what an introduction. Dig! bears out every parental warning about rock rotting the brain, with sex, drugs, fruity language, prison, mental illness and cowboy hats all figuring. Narrated by Dandys frontman Courtney Taylor, the film follows seven years in the interwoven careers of the Dandys and their San Francisco rivals the Brian Jonestown Massacre, who founder as the Dandys climb the success ladder. It's a gripping, depressing 90 minutes, and if I reveal that the Dandys, with their spartan Los Angeles apartment and 500-mile drives from gig to gig, live the life of Riley compared with the BJM, you'll have an idea of the wretchedness of the latter's existence. The film has been called "the real-life Spinal Tap", a tag justified by scenes such as the one that culminates in BJM singer Anton Newcombe wailing, "I've broken my sitar!"

While the Dandys don't come out of it that well (and Newcombe barely comes out at all, sinking into addictions), it has raised their profile. When their fifth album, Odditorium or Warlords of Mars, appears next month, it is guaranteed to attract more attention in their homeland than the previous four combined. In Europe, they can expect to increase an already healthy following. The album is daring, far removed stylistically from 2003's electro-glam Welcome to the Monkey House. They've been inspired by the surging psychedelia of Primal Scream and the Happy Mondays, which will give America's "modern rock" stations something to puzzle over. The album title sounds like a cross between early Bowie and late Iron Maiden, but is actually named after a studio - the Odditorium - owned by the band in their home town of Portland, Oregon.

So Portland must be pretty proud of you Dandys these days, eh? "I had a schoolgirl freak out on me the other day, which was cute," offers Zia McCabe, the keyboardist. In Dig! she parties as recklessly as her male bandmates, but is a reformed character now - married and with a year-old daughter. Apparently, typical McCabe interviews used to involve partial nudity; now she passes the time making scoochy faces at baby Matilda.

"Aah, it didn't really change anything," says Peter Holmstrom (guitar; cute and laconic). "People who knew us went to see the movie."

"It didn't get anybody else into us. The film got press [in America], but only 30,000 people went to a theatre to see it," says Taylor. "It was a critical success, but we're only in the Portland press, like, if Bowie's in town and talks about us. The only person from Portland who's famous is Gus Van Sant." He pauses. "Oh, and the drummer from Weezer."

Everything Taylor says is so laced with irony he could be Neil Tennant with a skater-boy accent. McCabe, Holmstrom and Brent DeBoer (drummer) let him dominate, occasionally looking up from lunchtime salads to contribute a sliver of dry banter. It's quite a surprise. The Dandys are accomplished musicians and hedonists, but who'd have thought their talents included Brit-style wit?

It's certainly not evident in Dig!, where they direct their energies towards touring, carousing and trying to save Newcombe from himself. It's not an edifying sight, particularly spread over seven years. You have to credit director Ondi Timoner for her perseverance, considering that when she started filming, in 1996, neither band was more than a small local attraction. It seems to have been a labour of madness, but it paid off as the Dandys began to attract acclaim for their drug-inspired take on things and found themselves filming the video for Not if You Were the Last Junkie on Earth with fashion photographer David LaChapelle. Meanwhile, Newcombe managed to defer success by working himself into unfocused rages, often on stage.

"It was a huge task with no end. Every new album, that was going to be the cut-off point, it'd be done," says McCabe. Taylor adds: "Nobody ever thought she'd finish [the film]. Then she called me on the way to the airport and said she was finally finishing it, and wanted me to narrate it. I said, 'Yeah, right, after eight years?' But she really hassled me, and they got me in to do it."

How did Taylor, who fills in the "occupation" section of immigration forms with "rocker", feel about seeing himself on screen? "Everyone in Europe loves the movie because it makes people feel hopeful, somehow, but it makes me feel uncomfortable and exposed. But what do I know? My favourite part," he says sweetly, "is where Zia wipes something from my face. We're like monkeys grooming each other, 'cos we're like a family."

They still live in Portland, a Pacific Northwest city 150 miles south of Seattle. "Portland has pretensions to being culturally informed," Courtney drawls, clearly disagreeing. Their main tie to the place seems to be the Odditorium, which was financed by Taylor's royalties from the single Bohemian Like You. This typically scathing bit of power-pop was used in a Vodafone ad in 2002, and earned Taylor - the band's chief songwriter - around $1.5m. He bought a quarter of a city block, and turned it into a complex with space for recording, film editing and web design. Amazing how much you can make from one advert, Courtney. He smiles lazily. "I got enough to hire my cokehead friends to design it."

The Dandy Warhols spout this kind of thing all the time, because drugs were (or are) a definitive force in their lives. Even now, at midday, they're passing around a dinky pipe full of something that makes Taylor slump into the sofa cushion, his eyes half-closed. McCabe, now a solid maternal citizen, watches nostalgically. "I always looked great strung out - dead white, with red lips." Taylor counters: "I've had hangovers where I looked better than when I wasn't. And now I look like Bill Clinton."

He doesn't. He looks like a slightly raddled college boy. He refuses to reveal his age, but McCabe helpfully announces that, at 30, she's the youngest. She was also "the first to get married and the first to have a baby". But while she's so settled that she's even considering a career as an estate agent when the Dandys finally finish, Taylor is still the rakish rocker with a sideline in existential misery.

Slouching even further back, he nods almost vigorously. "I haven't moved on past self-loathing and self-doubt. If you move past those things, you're done, you're Sting. Sting Collins. Every time I think I've grown up, I do or say something that shows I'm a complete child." Indeed, Taylor "quit" the band in a fit of pique during their last tour, and around that time said he often felt suicidal. Was that for effect? "I never say things for effect. It depends on the day. I felt dark about things this morning, but, I mean, you have to have perspective. This is our job!"

There's a sense, though, that even Taylor has moved on. He's no longer the person who wrote hits based on choruses such as "Heroin is so passe". Heck, he even has advice for Pete Doherty. "He looks great, all pasty and skinny, but he probably has two years left of looking great. I hope when he eats and drinks, it's filet mignon and a late-'60s Bordeaux." The band's last gasp of real debauchery probably pre-dates 2003's Monkey House album, which was produced by Nick Rhodes of Duran Duran. It was a crunchy glam extravaganza that inexplicably reached only number 20 in the UK, which puts pressure on Odditorium to better it. Dig! will undoubtedly give it a boost, and its prospects are also helped by the current vogue for guitars. The first single, Smoke It, is a zoo-style psychedelic free-for-all that doesn't resemble anything they've done before, but will fit into the chart alongside the likes of Kasabian and Gorillaz. "It is so whacked off on its own trip. It's the culmination of everything we learned on the other albums," Taylor says with satisfaction. You may not have to lock up your daughters any more, but the Dandy Warhols are not ready to become Sting Collins quite yet.

· Smoke It is out on August 29. Odditorium or Warlords of Mars is out on September 12