John Hodge combines a career as a doctor with that of a successful screenwriter - the title of his latest, A Life Less Ordinary, could sum up the man himself

The son of doctors, John Hodge left Edinburgh university in 1987 qualified to follow in the family tradition. But while his white-coated contemporaries were writing prescriptions, Hodge worked on a different kind of "treatment" altogether: a screenplay for a film called Shallow Grave. Hodge was back on the wards even as the film began shooting, but has continued moonlighting in the movie business ever since, adapting Irvine Welsh's Trainspotting and completing his second original work, A Life Less Ordinary, which is released next week.

A wild romantic comedy, the film stars Ewan McGregor as Robert, a janitor who kidnaps rich girl Celine (Cameron Diaz). Hodge "wanted to try something less dark, more light-hearted" and at first sight the film does seem different from its mordant predecessors. Look closer, however and you can diagnose traces of the same old sensibility. So there are angels? These are the kind that machine-gun your windscreen. There are head wounds and fights, not to mention the loving close-up of a bullet gouged from flesh.

Perhaps Hodge's morbid streak stems from his other profession? "I got some of the anatomical details for Shallow Grave from working in a hospital," he concedes, "but not the inspiration." But he admits that on returning to the NHS he did notice "everyone had a really sick sense of humour."

Hodge's latest is a film which plays on stereotypes of gender and romance. It is a love story with the conventional couple turned on their head, with Robert passive, dopey and vulnerable and Celine razor-sharp, a "victim" who orchestrates her own kidnapping. "Trainspotting was very much a guys film," says Hodge. "I wanted to redress that balance, write something with really strong female characters." So, along with Celine comes Holly Hunter's O'Reilly - more of a vigilante than a guardian angel. "I didn't write the part for Holly Hunter," says Hodge. "But it was her voice and her acting style I had in my head as I was scripting it. She's also very small which was a good counterbalance to the fact that O'Reilly is really hard." He did, however, tailor the part of Robert for McGregor. "I wanted to write a character closer to the real Ewan. He's much more like Robert than Renton, which is a relief to everyone around him." Originally set in Scotland, Hodge found his story better suited to the psychological and physical landscape of America. "A Life Less Ordinary is about extremes of behaviour and personal status. The kidnapping just wouldn't have worked in Britain because it's too small. It's hard to go into hiding here." Growing up with American films and TV, Hodge had little problem writing in an American idiom, but admits "the most exciting moment for me in the whole process was hearing American voices read the script."

Now working on an adaptation of Alex Garland's The Beach (a kind of Lord of the Flies for Generation X), Hodge has also written a spin-off novel of A Life Less Ordinary. "I only had a month to do it, but it was interesting because it allowed me to explore the lives of the minor characters. You have to think through all the histories of these parts for the film, but so little of that ends up on screen."

After completing A Life Less Ordinary, Hodge spent six months as a senior house officer at St George's in Tooting, but says he's unlikely to return to medicine full-time, content to provide the film industry with a new kind of script doctor.

A Life Less Ordinary is on release

this weekend