Medical student drama is, on the whole, a dish best served with vast amounts of alcohol. Not by accident do medical revues consistently win the aptly named Snakebite Award for the worst show at the Edinburgh Fringe. Back Passage to India, Beverly Hills Plop, Room With a Poo, On Her Majesty's Secret Cervix, Brownfinger - all have made the gloriously unsuccessful transition from med. school bar to public stage, and all focus for their laughs on that little area in-between the femurs and slightly in front of the coccyx.

There are several theories for the medic's obsession with all things lavatorial. For a start it's not just medics. Excretion is funny, perhaps not to you, but to enough people to enable such comedy greats as Rik Mayall and AA Milne to keep the belly laughs rolling in. Bowel humour allegedly has its cultural roots in public school, courtesy of matron who insisted on lining the boys up every morning and force-feeding them syrup of figs if they hadn't "been" yet. Medical school is, after all, just an extension of public school - the dean is head boy, the consultants are prefects and everyone else is a fag. And the matron theory of bowel humour ties in well with the golden rule of doctoring: if in doubt, blame it on the nurses.

The other hallmark of medical humour is the tendency to aim at targets below you in the hierarchy: nurses, patients and diseases. In a patronage system, you'd be a fool to stand up on stage and say, "My training's abysmal" or "Mr X the surgeon can't tie knots and sexually harasses his staff." Far safer to have a good giggle at cancer. Of the two student revues I've seen recently (The Wizard of Jism and Fish Genitals Smell of Humans?), there was only one political gag - "This show is sponsored by South Birmingham Health Authority" (which was pounds 50m in debt at the time). The rest was about fish, genitals and diseases - the Para-Olympics sketch with synchronised epileptic fits, that sort of thing. Rather perversely, each performance was for charity, as if giving money to the British Epilepsy Foundation justified the offence.

Again, it's not just medical students who are guilty of diseasism. Tony Gardner and I started Struck Off and Die in 1990, when we were qualified doctors, and we've made some distinctly unhelpful illness gags along the way, most noticeably by satirising ME support groups on Radio 4 -"We're organising a sponsored walk." "Anywhere special?" "Just down to the end of the coffee table and back." In our defence, among the bagfuls of death threats were some letters from ME sufferers who enjoyed it but I still feel deservedly guilty, and unsafe, when I see one in morning surgery.

Even those lowly nurses can't escape blame. I once asked three student nurses working on a care of the elderly ward to write a song for the Christmas Show. They rewrote Merry Christmas, Ev'rybody, to the chorus of, "So here it is geriatrics, Ev'rybody's had a stroke, Let's get the turkey out, And see how many choke."

None of these hardened attitudes would have reached the wider public if it wasn't for Cardiac Arrest, written by junior doctor Ged Mercurio. As an angry, black dollop of compressed realism, the first series contained all things bad and rather overdid the "blame it on the nurses" line - portraying Angels for the first time on British television as a bunch of clock-watching, bolshy witches. Initial viewing figures of 10 million suggested the public might be up for it, but they fell away sharply. We Brits, it seems, prefer the relative cosiness of Casualty and its happy band of carers.

Ged is just the sort of bloke you want to get in there and fight the system. Instead he decided to get out of medicine, buy a Porsche and disappear to Hollywood. I can't say I blame him. Tony, too, has swapped the stress of medicine for the insecurities of acting, but medical schools, against all odds, still nurture rare talent. Last week, and after three pints of Snakebite, I cautiously went to see a student play, nobody, anybody, somebody.

A piece of writing with no bums, nurses or diseases to fall back on is the ultimate challenge for any scribbling medic. This attempt, a comedy about relationships, was brilliant - more men behaving sadly than badly - and above all funny.

Afterwards, the writer Ross Overshott was at pains to point out he'd made pounds 200 for charity. I was more interested in his future. "I suppose this means you want to get out of medicine, too?" "Not at all. I want to be a psychiatrist." And yes, there is a difference.