If the idea of Ozzy Osbourne writing a health-and-wellness column seems ludicrous — I mean, this is Ozzy we’re talking about, the inchoate wet-brain that you’ve seen shambling across your teevee screen — well, that was the general idea. The Sunday Times and Rolling Stone figured it was stunt-casting when they signed Ozzy for the job. It was a conceptual goof, on a level with hiring Larry King as a marriage counsellor.

But who’s laughing now? I mean, have you seen Ozzy lately? It’s been almost a decade since The Osbournes debuted, cementing the public image of Ozzy as a palsied, gibbering wreck unmanned and distraught by the rigors of a task as basic as making a cup of tea. But no jive, Clive — the 2011 model Ozzy is jacked. He’s dried out and tightened up, ditching the booze, pills, cigarettes, and red meat and logging some serious time in the gym. At 62 years old, the dude runs a buck seventy-five, for cryeye, and still plays a hundred shows a year at three hours a night. Talk about your iron man.

So in that light, Ozzy’s new gig makes a twisted sort of sense. Now “Rock’s Ultimate Survivor,” as he’s billed, is sharing his observations and advice for a life well-lived in the new collection Trust Me, I’m Dr. Ozzy, out today and co-written with Chris Ayres. It’s a hodge-podge of previously published columns and new material, organized thematically and fleshed out with newly-written interstitials and introductions, along with a selection of quizzes and sidebars covering a miscellanea of medical oddities, quack remedies, and farts. It’s the sort of thing you might find in a back issue of Men’s Health, if the editors of Men’s Health didn’t keep their perverse, sarcastic sides so carefully hidden.

The Q and A format suits Ozzy down to the ground. It’s not that he’s incapable of giving a straight answer — his advice is generally precisely the sort of common sense you’d expect from a reasonably well-informed layman — but he’s rarely content with that, instead spinning his answers into anecdotes and one-liners. The fascination of Ozzy’s public persona is that he seems to have no filters. With Ozzy, what you see is what you get, and Trust Me is filled with passages directly referencing his checkered past and personal struggles with substance abuse, anxiety, and depression. He’s well-informed about health issues, he tells us, because he’s a raging hypochondriac; sexual impotence, a side-effect of his regime of antidepressants, is another recurrent punchline. The effect is sometimes a little cringey, but more often laugh-out-loud funny, as with an account of a time in the 1980s when Ozzy cured athlete’s foot by rubbing cocaine on the affected area. Street coke, he reasoned, was cut with so much foot powder in those days that it was probably more worthwhile to put it between his toes than up his nose. “The only problem was the price,” he quips. “It worked out to about three grand per toe.”

Of course, the format wouldn’t work if the questions were simple and straightforward. Fortunately, Dr. Ozzy’s correspondents give him plenty of material to work with:

Can you really get drunk by soaking your feet in a tub of vodka?

I recently swallowed a fly while horseback riding: Will it give me an awful disease?

My doctor told me I have high cholesterol: Does this mean I should stop taking cocaine?

You can’t make this stuff up (although one has a sneaking suspicion that somebody did).

A surprising number of correspondents are in search of advice on love, family, and friendship, and Ozzy does not disappoint. At first blush, he’s an unlikely relationship guru given the televised chaos of his own home and family — but again, appearances are deceiving, and “dysfunctional” is a relative term. Ozzy and Sharon’s marriage has surely been tumultuous, but they’ve stayed together, stayed in love, and stayed friends for a long time now, all while trying to raise their kids to be sane and functional. That’s hard enough for us non-Hollywood types; but they’ve managed it through various health and substance problems, career ups and downs, and a run through the media pressure-cooker. You could do a lot worse.

What’s most disarming about Trust Me, though, is the pleasure that the good Doctor takes in his role. Though he refers to himself (with tongue in cheek) as “the Prince of Darkness,” Ozzy has always understood that it’s possible to make music with an evil edge without feeling the need to be evil oneself. An Ozzy Osbourne show has more pie-wide grins, more positive vibes, more cries of “God bless you!” than your typical Billy Graham crusade. The man loves what he does, and he loves his audience — and in between the laughs, he manages to slip in a little wisdom and a lot of comfort. Ozzy’s black-humored riffs about the failures of his own aging body venture occasionally into “TMI” territory, but their very irreverence lends the reader courage in the face of the worrisome subject of mortality. That’s the upside of taking advice from a rock ‘n’ roll survivor (even if that advice usually boils down to “Maybe you should talk to a real doctor about this”). No matter what you’re going through, chances are Ozzy Osbourne’s been through it first and worst.