Glasgow GP Dr Margaret McCartney is on a crusade against what she calls "sexed-up medicine".

It's an arresting phrase, and she says there's a lot of it about, but what does it mean?

The term, as she uses it in The Patient Paradox, her first book, covers everything from the oversold promise of preventative scans for cancer and "full-body MoTs" to charities pushing the cause of the week or pharmaceutical companies putting out misleading press releases.

It is political, too – given the argument she makes that some ailments are better treated as social problems than being viewed as medical. "We try to treat poverty with pills," she says. "You need to treat poverty with money."

Dr McCartney hasn't published a book before, but her writing is regularly seen in leading journals and newspapers where she has won awards for her medical journalism, as well as to an enthusiastic following online, where she blogs and tweets. She combines all this output with working part-time as a GP in an Anniesland practice – although she stresses that she never writes about her patients.

Google her name, and you'll find outspoken commentary on – among other things – the Coalition Government's system for medically assessing disabled claimants and the need for all medicine to be evidence-based.

Last year she hit the headlines after commenting on the widely-held, but erroneous, belief that the average person needs to consume 1.5-2 litres of water a day. "Thoroughly debunked," she was quoted as saying.

The Patient Paradox has allowed her to pull together a number of related themes into a coherent argument she explains. "I've been writing about issues such as screening, overdiagnosis and professionalism for ages, but never had a chance to join it all up."

However, its roots go back roots a decade ago, when she was on maternity leave for her eldest son (she has three children). "I saw an advertisement urging people to have a CT body scan, with a patient saying 'I feel so healthy after it'," she explains. "Some are making a lot of money out of people's fears about their health."

But all screening can do harm as well as benefit, she says, and much is unnecessary.

"People mostly know if they are unhealthy. They may be overweight or underweight, or they smoke, or they don't. Most of these things are really straightforward.

"In the UK, social inequality is the biggest determinant of poor health and overmedicalising people is not going to help with that."

The biggest area in which the health of Scots can be improved rapidly and effectively is by tackling those inequalities and preventing future ill health, Dr McCartney says.

Instead, she argues, people are being put on drugs, such as statins (cholesterol--lowering tablets), including poor people deemed at higher risk because of their postcode or dietary factors.

"Too often we are not looking at the real issues, offering a medical response to a social problem."

Meanwhile, the treatments have side effects. Most people on statins won't benefit, she points out. "For every 167 people we treat with statins, one will develop diabetes as a result. One in 60 people treated with it for five years will avoid a heart attack – 59 people who take the drug won't get that benefit. One in 268 will avoid a stroke – so 267 of them won't see that benefit."

However the system is skewed against such honesty. GPs are paid for controlling risk factors, prompted by computer screens that remind them to do so. This can mean statins, smear tests and breast-screening or other scans.

What is good for a population may not be good for an individual, she points out. "Doctors have become deprofessionalised so that we see patients as a list of indicators we have to satisfy."

While many people might think that finding a cancer, for instance, which can then be treated, is a self-evident good. But this ignores the risks of the test itself.

Excessive scanning leads to people being treated because of "false positives", but also for problems picked up which would never have harmed them, she says. Breast scans are a classic example. "If 2000 women are screened for 10 years, one of them would avoid death from breast cancer, but we will also treat 10 women who were never going to be harmed."

The answer she proposes is not to stop smears, scans or prophylactic drugs, but to be more honest with patients about their limitations.

"For me, good medicine is sitting with patients helping them to make difficult decisions. We should be able to respect patients as competent individuals and help them to make the right decisions."

Instead, targets become tied up with what a good doctor is in the modern NHS –north and south of the border, she points out. "The GP contract is national, so we have the same tickbox nonsense in Scotland."

The book contains much more, in similar punchy style, but backed up with extensive notes and references to research – unlike the misleading press releases from drug companies which sex up a treatment's effectiveness by talking about relative risk (for example ("it cuts your risk by 50%") rather than absolute risk ("it cuts it from two in 1000 to one in 1000").

She is also critical of charities, whose campaigns to raise awareness of a range of conditions can feed fear, and often depend on similarly hyped statistics. "It is understandable that they want their moment in the spotlight, but to get that people are having to sell their message in sexier and sexier style," Dr McCartney says.

"The result is, for example, that young women asked by researchers about breast cancer overestimate their risk of getting it, while they underestimate the chance of successful treatment.

"A GP will see a woman who is terrified in case she gets breast cancer, but she may not be worried about her binge drinking or the fact that she's overweight."

The Patient Paradox of the title is that clinics are full of healthy patients, risking harm through needless diagnosis, while the genuinely ill have to be persistent and determined to get help. What is needed is a return to a less mechanistic idea of what a doctor should be, the book argues.

"Most doctors will say they go into medicine because you feelthey have a vocation. By the time they come out of training that has been almost dismissed, and they are given a computer programme and a set of targets. I'd like us to reprofessionalise," Dr McCartney says, with a sly nod to the SNP's deputy leader and health minister Nicola Sturgeon. "If Nicola's reading..."

The Patient Paradox is published by Pinter and Martin today, priced £9.99