It was Voltaire who said the art of medicine lay in amusing the patient while nature cures the disease. In the 21st century this valuable epigram has been turned on its head. Medicine is increasingly concerned with persuading the patient that nature has cursed them with a new disease that only doctors may cure.

The current issue of the British Medical Journal provides a teasing, thoughtful, insightful tour of the many ways in which life has become medicalised. Pharmaceutical companies sponsor disease definitions in order to provide an ill for every pill. Selling sickness is profitable. The BMJ dubs it "disease mongering".

I remember the press launch of a pill for shyness, repackaged as "social anxiety disorder", which I attended a few years ago with Ian Jack, then a columnist on this paper and now the editor of Granta magazine.

Ian Jack is a gentle, diffident man and he was shocked by what he heard. He wrote a wonderful piece about the role of such a pill in "the tongue's great age" when "confident speech and confident appearance matter more than at any time in history." It was clear that, while a few people are genuinely disabled by intense fear of social situations, the pharmaceutical company had spotted a marketing opportunity and had set about exploiting it.

In Australia, where a different company was promoting a different drug for the same condition, a press release claimed one million Australians suffered from under-diagnosed "social phobia". In Europe, the magazine Pharmaceutical Marketing singled out social phobia as an example of the drug industry's success in shaping public perceptions.

The marketing of fear and inadequacy are simple ways to boost drug sales. We have seen it with osteoporosis – "Women – go for a bone density test now" say the ads – even though the benefits of drug treatment for low-risk women are small and may be outweighed by the risk of side effects.

The medicalisation of sex has made Viagra the world's most popular medicinal drug – but does this reflect a genuine need or people's increased expectations in our sexualised culture? On America's west coast, clinics are offering women gynaecological laser surgery. Genital enhancement – the so-called "designer vagina" – involves liposuction, tightening of muscles and clitoral repositioning. Women may come to share with men a whole new area of anxiety.

There is another side to this argument – that the public need to be made aware of treatable conditions so they do not suffer in silence with potential damage to their long-term health. The improvement in survival from breast cancer over the past decade is in part due to the efforts of the breast cancer lobby in increasing vigilance among women and doctors to ensure treatment is delivered early.

Depression, too, is a condition that most psychiatrists believe is under-diagnosed and under-treated, and which leads to many avoidable suicides each year. For five years the Royal College of Psychiatrists ran a campaign to increase recognition of depression.

But as Ivan Illich warned a quarter of a century ago, we should beware of medicalisation that saps the will of the people to suffer reality. Death, pain and sickness are part of being human. The economist Amartya Sen has observed that the more a society spends on health the more likely are its inhabitants to regard themselves as sick. This explains the paradox that people in America feel less well than those in Bihar, India. Too much medicine diminishes us.