For 11 years, Maria Saunt felt a complete absence of any sexual desire for her husband, Peter. Her frigidity nearly tore apart their marriage.

'After the birth of our son, I didn't want to know about sex,' said Maria, a 39-year-old London businesswoman. 'It wasn't that I felt revulsion, it was a complete absence of desire or interest. Peter and I didn't talk to each other about it and it was very, very difficult for him to understand.'

She finally resorted to a herbal remedy, ground-up Nicaraguan coffee beans, which she says restored some enjoyment into their lovemaking and saved their marriage, but she regrets that they did not go for counselling to talk through the problems, which she feels stemmed from confusion and fear surrounding her new role as a mother.

Maria (not her real name) is one of thousands of British women said to suffer from female sexual dysfunction, (FSD), which incorporates a loss of libido or desire, difficulty reaching orgasm and sometimes painful sex.

But experts last week accused pharmaceutical companies and their researchers of cynically creating the disorder to provide a multi-million dollar market for new drugs.

An editorial in the British Medical Journal suggested that, far from being a serious condition afflicting up to 40 per cent of women, this 'disorder' was dreamed up as a way of making enormous profits from sales of tablets and creams to unhappy, mostly middle-aged women.

At the heart of the controversy are seven meetings over the past five years, sponsored by drugs companies, at which the subject of FSD began to emerge as specialists - some receiving funding from the companies - tried to define it. The BMJ describes FSD as the clearest example yet of 'the corporate-sponsored creation of a disease'.

The allegations come as the drugs giants compete harder than ever to find the magical medicine that will provide fulfilment for women whose sex drive is no longer there. The condition's characteristics are said to include a loss of interest in sex, less enjoyable sex, diminished sensation and inability to achieve orgasm. There is no doubt that thousands of British women suffer these problems, but evidence that it is a genuine medical condition remains scanty.

The BMJ's criticism has shocked the medical community, because it suggests that researchers are in league with the pharmaceutical giants, and creating bogus diseases.

But the arguments touch other areas where there have been questions over the absence of firm evidence or proof. In children, there is concern that attention-deficit disorder and attention-deficit hyperactivity disorder are names given to behavioural problems the root cause of which may not be any organic disease. Some worry that thousands of children in the UK are being diagnosed with the condition, and put on the stimulant drug Ritalin, with no firm long-term study to prove that it works.

Another such disorder may be the male menopause. Although the idea has become increasingly fashionable, with men taking extra vitamin pills and even having testosterone injections, psychologists believe it is simply the latest term for what used to be called the midlife crisis.

Pfizer, manufacturers of Viagra, insist that FSD really exists. They would say that: they are holding trials of their drug on women in Kent, to see if it can help. Their medical director, Dr Mitra Boolell, says there is no shortage of women willing to be recruited for their trials, but firmly denies any attempt to create an artificial condition to boost profits.

'Long before Viagra was launched, the condition was being recognised by various organisations,' he said. 'In 1994, the American Psychiatric Association, defined it in their own terms.

'This is a complex condition, caused by emotional, psychological and hormonal factors as well as muscular disorders. We have been able to show that a proportion of women potentially may be able to benefit from the drug, but the research is at an early stage. We have a huge number of women wanting to take part in our studies, reflecting what is happening in real life.'

One undeniable aspect of this controversy is that the companies are in a billion-dollar race to develop a therapy that would give women worldwide a sexual pick-me-up. It is not simply Viagra being tested in the laboratories. Hormone patches, creams and nasal sprays, as well as other pills are all in the offing because of the enormous stakes involved.

Viagra created an enormous market for erectile dysfunction. Sales of drugs to treat male impotence stood at around $2 billion last year and are expected to top $4bn by 2004. The question is which will become the first company to market the female equivalent.

If the BMJ doubts that FSD exists, what would it make of a new American definition, known among urologists as Female Sexual Arousal Disorder? A Californian company, Vivus, is conducting trials of a cream, Alista, aimed at helping women to become properly aroused by aiding blood flow to the clitoris. The second stage of its clinical trials showed that it appeared to help some patients, although the number in the trial was relatively small. Scientists at another US company, Palatin Technologies, have tested a nasal spray which they say can send women into a state of sexual arousal.

One problem for doctors is that female sexuality is still something of a mystery. The problem is not mechanical, but a more mysterious interaction of psychological, hormonal and possibly physiological factors. Because so little research has been carried out on women who have lost their libido, it has become difficult to form even a proper definition of the condition. Scientists say it is more common among menopausal women and is known to be a side-effect of diseases such as diabetes, or of cancer treatment.

Leonore Tiefer, professor of psychiatry at the New York School of Medicine, is hugely sceptical about the pharmaceutical industry.

'The idea that 43 per cent of women suffer from sexual dysfunction is totally fallacious,' she said.' That figure came from one question in one survey and has been spread as thinly as butter on bread ever since.'

Accusing the scientists of being 'obsessed with genital blood flow', she said: 'I don't believe anyone loses interest in sex purely because of that.' To her, the prospect of 'magic bullet' treatments diminishes any true understanding of female sexuality, serving only men's interests.

Emotional dissatisfaction with their partner is seen by many doctors as the real reason behind many women's unhappiness, and some say the new diagnosis may simply reveal the scale of relationship difficulties.

There is no simple, easy way of untangling sexual difficulties and GPs increasingly suggest psychosexual therapy or proper marriage guidance as the best way forward.

But the Impotence Association, which campaigned for Viagra to be widely prescribed to men with erectile dysfunction, is adamant that FSD is a real condition and that thousands of women are suffering, mostly in silence. Whatever the truth is, when its helpline number is published, it is deluged with calls from women who do not know what is wrong with them, according to its director, Ann Tailor.

'Couples are very reluctant, very embarrassed to talk about it. There's this myth that women discuss it among themselves, but they don't. They go to the GP who tells them it is their age, or a stage they are going through, instead of taking it seriously and referring them to a specialist.'

She is dismissive of the BMJ article, pointing out that scientists in all branches of medicine rely on industry grants, and stressing that FSD can be both a physiological and psychological condition.

'But to dismiss it as fictional does a huge disservice to all the women who have to live with this,' she says.

· Do these diseases exist?

Female sexual dysfunction

Yes, say some psychiatrists and drugs companies, who think it is a complex pattern of emotional, hormonal and physiological problems leading to lack of desire in sex, and sometimes pain.

No, says the British Medical Journal and other specialists, who say that relationship difficulties and psychological problems are the real cause.

Male menopause

Yes, say some specialists who point to the drop in testosterone levels as men hit their mid-40s.

No, say some psychiatrists, who argue there is no evidence for men suffering the equivalent of the female menopause.

Attention-deficit disorder

Yes, according to many child psychiatrists who believe it is a set of behavioural problems that can wreck a child's life unless treated, sometimes with drugs.

No, say therapists who believe that talking to the family is better than a 'chemical cosh'.

Gulf war syndrome

Yes, say US psychiatrists and thousands of soldiers, who believe the insomnia, fatigue, muscle pains and fevers they have suffered must spring from some aspect of the conflict.

No, say most British psychiatrists who feel it is a collection of symptoms with different causes.

Advanced sleep phase disorder

Yes, say scientists who claim that much of the night-time insomnia in the elderly is caused by the body clock becoming out of sync.

No, say other physicians who argue that sleeplessness is simply one of the signs of ageing.