It's fairly well known that women need rather less alcohol to get drunk than men do because they have less alcohol dehydrogenase, the enzyme that breaks down booze, in their stomachs. Probably less familiar is the recent discovery as to why heavy-drinking women are also more at risk of liver damage.
Researchers at Pittsburgh University found that alcohol has quite different effects on the way various genes are expressed in the bodies of males and females. (Very broadly, genes produce proteins but all sorts of factors, such as having a lot to drink, can increase or reduce how much they make. Those variations are known as gene expression.)
Using a number of unfortunate rats, which were force-fed alcohol, the scientists found that males have an apparently random and unfair advantage when it comes to protecting the liver. Although heavy drinking affected the expression of far more genes in males than females - 27 versus six - the expression of several genes that make proteins that protect the liver was increased in males but decreased in females. The guess is that something similar may be going on in humans.
This is just one example of a whole new field of research into the different ways men and women respond to drugs. In fact, it's a basic principle of modern medicine that, if you turn up at the doctor's surgery in need of pills for pain or a heart condition, you'll get the same whichever sex you are. In a few years' time, however, such unisex treatment could seem ham-fisted.
Perhaps the most obvious difference in male-female physiology is the menstrual cycle, and fluctuations in female hormones probably underlie many of the variations in drug response. This month, more rat-based research suggested a distinct female response to cocaine, which could both put them at greater risk of addiction and reduce the danger of a drop in blood supply to the brain. Scientists at the University of Michigan found that a combination of oestrogen and cocaine made females 25% more sensitised to cocaine - that is, more likely to develop a craving for it. However, the higher levels of oestrogen that women have during the first part of their menstrual cycle makes their blood vessels more flexible. One of the dangers male cocaine addicts face is a restriction of blood flow to the brain.
The hormonal changes driven by the menstrual cycle have long been a problem to researchers studying new drugs because they made the results more difficult to interpret. The result was that, until quite recently, women were simply left out of them.
It may come as a surprise to learn that until about 10 years ago, nearly all drugs, even ones aimed specifically at women, were routinely tested only on men. This was partly because of genuine fears about safety. The thalidomide tragedy had made everyone very sensitive to the unsuspected damage a drug could do to the foetus, so doctors were worried that a woman might get pregnant while taking a new drug. But it was also to prevent women's monthly cycles muddying the analytical water. By the early 1990s, however, it had become increasingly clear that men and women not only sometimes responded differently to drugs, but also could have quite different symptoms, too.
Take what happens with pain. Women are three times more likely to suffer from migraine and six times more likely to develop a chronic muscle pain called fibromyalgia, while there's a considerable difference in the way men and women respond to analgesics. Women find more relief if they are given painkillers based on opium - known as "kappa opiods" - while men do better on ibuprofen.
"Findings like these could revolutionise the way we understand health and disease in both men and women," says Phylis Green berger, of the Society for the Advancement of Women's Health Research. In 1993 it was made a US legal requirement for women to be included in trials. But a report last April from the US General Accounting Office, concluded: "Health care for women may suffer because researchers overlook important differences between the sexes in clinical trials."
The report found that while the large-scale drug trials were now made up of 52% women, the smaller, earlier trials for toxicity and dosage only had, on average, 22% women. Concern about this bias is not just academic. Of the 10 prescription drugs withdrawn from sale since 1997 because of adverse reactions, eight posed greater risks for women than for men. Four of them increased women's risk of developing a dangerous irregular heartbeat. Heart attacks provide a good example of the way ignoring gender differences can be really damaging.
Women suffering from heart attacks do not always show the classic male symptoms - severe squeezing chest pain and a feeling of fullness in the centre of the chest. Instead, they are more likely to have "silent" symptoms such as a shortness of breath, fatigue, discomfort, nausea, dizziness or pain in unlikely places such as the jaw.
One result of women's hidden symptoms of heart disease is that they are likely to have less effective treatment for heart attacks. For instance, the latest high-tech treatment for patients whose heart rhythms are seriously out of synch, is an implanted defibrillator, which can correct them electronically. At the American Heart Association meeting last year, however, it was reported that women are half as likely to get one as men. A recent report in the British Medical Journal found that although a higher proportion of women had raised cholesterol levels, men were more likely to be given cholesterol-lowering drugs. As it turns out, these are drugs that benefit men and women equally.
One of the big promises made after the human genome sequencing was that drugs could become more precisely targeted to take account of genetic variations - so reducing side-effects. Distinguishing between a man and a woman requires no hi-tech testing and could start saving lives now. We are some way from that yet, though: 40% of current applications for trials of new drugs make no provision for recording the different responses of men and women.
