Terri Paddock is unimpressed with today’s therapy culture, which sees people as “broken things that need to be fixed”. As an American living in London, she has found it depressing to see how fast that mind-set has spread across the Atlantic and taken root here in recent years.

So it is ironic to realise how deeply therapeutic it must have been for her to write Come Clean, a harrowing novel for teenagers about a girl who is locked up in an American boot-camp-style addiction rehab centre, where humiliation and abuse are the order of the day.

“I borrowed a friend’s flat in Monaco,” she says, “and wrote 60,000 words in a week. One day alone I wrote 20,000. I hardly slept. I hardly ate.

Writers sometimes talk about being a channel. It had never happened to me before, but this just seemed to pour out of me. At times I was writing it with tears streaming down my face. I guess it had preyed on my mind for years.”

The novel tells the story of Justine, whose parents put her into a draconian rehab programme to sort out problems they assume must be due to drink and drugs, but which, in fact, centre on family issues. She has been torn away from her beloved twin brother; her father is an orthodontist whose world view is limited to the inside of people’s mouths; her mother has a weak personality and offers Tic Tac mints as a solution to all of life’s problems.

The programme itself - the main character in the book - is horrendous.

Justine is stripped and searched, then dressed in charity shop cast-offs and marched around by a counsellor holding her trouser belt loops. The daily sessions take place in an industrial warehouse, and consist of yelling, confrontations and tears. At night she goes home with one or other counsellor, where she is watched, even in the toilet, and locked into the bedroom to sleep. Counsellors are mostly more senior participants in the programme, which offers rewards for informing on others. Teenage readers will be fascinated by the ghastly detail: how it feels to be dying for a drink of water, or the humiliation of being denied a bra. “I keep gettingI confronted for misdemeanors,” Justine says. “I reached for a lunch-time Happy Meal before being told I could take it, I walked out of step with my belt-looperI I tried to indulge my vanity by looking in a car’s rear-view mirror. One day I’m told off for refusing to wear the shirt provided for me by my host family - a shirt I couldn’t wear because it was at least three sizes too small - and the next day I’m told off for trying to turn on the boys because I am wearing a shirt that’s too tight and shows off my breasts.”

Young readers might also think the climate of bullying and intimidation is exaggerated for the sake of the story. But they would be wrong. In a foreword, Paddock acknowledges that the book is directly based on a private anti-drug programme, Straight Inc, which flourished in the US in the 1980s, using the “tough love” approach of intense peer-group pressure, with added starvation, sleep deprivation and physical restraint.

Paddock herself wasn’t in the programme, but her troubled older sister was.

The author had to attend family and sibling meetings, was herself accused of “druggy” behaviour, and had countless young people on the programme come to stay at her home. As in the novel, the real-life host families had to keep up the regime overnight and agree not to expose visitors to television, pop music or other media. Paddock remembers “the locking in (of the visitors), the family rap round the dinner table. I wasn’t allowed to read newspapers, or have the television on when they were there, I wasn’t even allowed to mention the names of television programmes. I wasn’t allowed to have people over. One night, I remember, a girl drank a bottle of shampoo because she thought she would go to hospital and her friends would get her out.”

Her sister is now a successful businesswoman with a family of her own, and claims hardly to remember her time in the programme, while her parents don’t talk about it - “they know about the book, but they haven’t read it yet”. But Paddock felt sufficiently disturbed by her encounter to track down some “Straight survivors”. When she found their stories were “a thousand times worse than I’ve been able to convey in this relatively tame fiction” she decided to write the novel.

Straight Inc no longer exists. It was chased out of state after state by allegations of brainwashing, kidnap, rape and suicide. Lawsuits proliferated, and it finally closed its doors in 1993. But Paddock says some of the founders are still working under new labels.

Come Clean is the 34-year-old American’s second novel. The first, Beware the Dwarfs, was an adult novel, and her third will be about an obsessive theatre fan. She claims she is “lazy and undisciplined” about writing, which seems unlikely given that, by day, she runs a theatre website, which she co-owns and runs with her soon-to-be ex-husband, and by night she is often at the theatre.

She fell in love with London when she came here as a student. “I was living in Regents Park, it was a beautiful summer, there was a manI”. She moved over here and worked in high-tech PR and journalism before living and working in South Africa for a year. As she muses on her uncomfortable time there - the high walls, the tension, the security, the claustrophobia - it occurs to her that the tyranny of fear is pretty much the same wherever it shows its face. If young readers get that out of her book, as well as enjoying a compelling story, then her private writing therapy will have been more than worthwhile.

Come Clean by Terri Paddock is published by HarperCollins Children’s Books pound;5.99