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Six years after Caroline Criado Perez’s bestselling book Invisible Women drew a mass readership’s attention to the long history of sexist bias in medical research, it is shocking that women and their illnesses are still underrepresented in clinical trials. Analysis by the Guardian of data gathered for a new study showed that from 2019 to 2023, 282 trials involving only male subjects were submitted for regulatory approval in the UK – compared with 169 focused on women.
Health inequality is a complex and multifaceted problem. There are massive socioeconomic differences in life expectancy and infant mortality, as well as race inequalities – for example, in maternity and mental illnesses. These and other disparities, along with those relating to disability, can also be mapped geographically.
Women, on average, live longer than men, so in this sense men can be said to be disadvantaged. But in addition to the risks associated with pregnancy and childbirth, far more women have dementia, while survival rates from female- and male-specific cancers – and other diseases that affect the sexes differently – are highly variable.
The five-year period in this study, which was carried out by the University of Liverpool and the Medicines and Healthcare products Regulatory Agency (MHRA), was not necessarily typical. It does not reveal how funding was divided up. But taking on board these caveats, it is hard to see a benign explanation for there being 67% more trials investigating men’s health than women’s. This gap in research inputs could reasonably be expected to contribute to a disparity in outcomes further down the line.
This is all the more disappointing given recent progress in tackling women’s exclusion from health research. For decades, as Ms Criado Perez and others have documented, many clinical trials were conducted on male subjects only. Researchers preferred to avoid what they saw as complications associated with the female reproductive system, especially pregnancy – although experts now regard concerns that women’s hormones might skew results as having been wrong.
Ninety per cent of the UK trials in the MHRA study involved both sexes. It is not possible to compare this precisely with past practice, as the data has not been scrutinised in the same way before. But increased recognition of the variable effects of medicines on males and females has led regulators and funders to change their policies. In the US, the National Institutes of Health has required investigators to consider sex as a variable since 2016. In the UK, the Medical Research Council changed its rules in 2022. Since then, experiments conducted on animals have been expected to include both sexes – with limited exceptions (such as when the condition being studied affects one sex only).
The lack of medical research on pregnant women came to the fore during the pandemic, when many were unvaccinated and alarming numbers ended up in intensive care. Reluctance to test drugs on pregnant women is often linked to the thalidomide scandal of the 1960s, when thousands of babies were damaged by a drug given to their mothers for morning sickness. But while caution may be merited, among pregnant women themselves as well as researchers, there is no shortage of women who are not pregnant. The disparity in sex-specific research points to an anti-female bias. Ministers, funders, hospitals and the pharmaceutical industry should all be concerned.
