Hormone fluctuations throughout adulthood have also been cited historically as a reason for excluding women, as scientists argue this makes women more difficult to study.

Take heart disease — probably the worst-offending area.

Although women make up 47 per cent of the 7.6 million people in the UK with heart disease, they accounted for just 28 per cent of participants in 500 key heart trials carried out between 1996 and 2015, according to a Canadian study, published in Circulation: Cardiovascular Quality and Outcomes in 2018.

This simple and very convenient approach — using male data for females — we now know undermines the way millions of women are treated for potentially life-threatening illnesses, such as heart disease and cancer.

‘When it comes to prescribing drugs, a one-size-fits-all approach, based on male-dominated clinical trials, is not working and women are getting the short end of the stick,’ says Irving Zucker, a professor of psychology and integrative biology at the University of California, Berkeley.

In 2020, Professor Zucker carried out a review of more than 5,000 studies and found that when men and women are given the same dose of a drug, women experience side-effects such as nausea, heart problems, headaches and seizures nearly twice as often.

This is because, at the same dose, women had higher concentrations of the drug in their blood, and it took longer for the drug to be cleared from their bodies.

medicines regulator the Food and Drug Administration (FDA) did just that for the sleeping pill zolpidem, once researchers found that after eight hours, the recommended 10mg dose resulted in 15 per cent of women still having enough of the drug in their system to leave them drowsy in the day, putting them at greater risk of road accidents.

Meanwhile, the exclusion of women from clinical trials continues.

In a recent example, pregnant women were not included in the initial Covid vaccine trials.

‘Undoubtedly, some of these deaths could have been prevented if pregnant women had been included in clinical trials and we had collected data more effectively.’.

Trials should include the same proportion of women who are affected by the disease in question, argues Natalie DiPietro Mager, a professor of pharmacy at Ohio Northern University in the U.S., who wrote a paper on the issue in 2016 in the journal Pharmacy Practice.

Astonishingly, some of the biggest studies ever carried out on serious, potentially fatal, conditions, such as heart disease, did not feature a single female in their volunteer ranks?

study of more than 20,000 clinical trials, involving more than five million patients between 2000 and 2020, identified six areas where women remain under-represented relative to the numbers affected — cancer, neurology, immunology, urology, cardiology and haematology, reported the journal JAMA Network Open.

This, the researchers said, is concerning because cancer and heart disease are the leading causes of death among women.

Around 24,000 women die from heart disease each year in the UK, and 78,000 from cancer.

So why are women not taking part in — or being actively excluded from — clinical trials.

One major reason is that, following the thalidomide scandal in the 1950s and 1960s, when a drug for morning sickness in pregnancy caused severe limb defects in thousands of children worldwide, women of childbearing age were barred from trials until the early 1990s, amid fears of similar side-effects.

‘We should be justifying the exclusion of pregnant women in clinical trials, not the other way round.

Physicians’ Health Study, which started in 1982 and provided key evidence over 30 years that low-dose aspirin decreases the risk of a first heart attack (by 44 per cent).

Similarly, the seminal Multiple Risk Factor Intervention trial, which launched at the same time and looked at how lifestyle factors such as smoking and diet influenced the risk of developing heart disease, included no women in its almost 13,000 participants.

Yet both helped to shape treatment guidelines around the world for all heart disease patients — male and female.

And later this year, the Government will publish its Women’s Health Strategy, which is expected to demand routine collection of data in clinical trials to show if women and men respond differently to new drugs.

‘We are committed to ensuring clinical trials are representative of the affected population,’ says Professor Lucy Chappell, chief scientific adviser for the Department of Health and Social Care.

The Medicines and Healthcare products Regulatory Agency, the UK’s medicines watchdog which also oversees medical trials, is considering new laws to ensure more women and ethnic minorities are included in trials.

shows 72 per cent of trials fail to include any breakdown by sex in their results — so they have no data on whether women are affected differently to men.

Professor DiPietro Mager adds: ‘A lot still needs to be done, not just in enrolling women in clinical studies but analysing the findings.’.