Half the population, half the data: addressing the women’s health gap in clinical research

This article is part of our Biotech Review of the Year - Issue 13 publication.

Historically, women have been underrepresented in clinical trials. This is due in large part to the ‘male by default’ approach that has been taken in research and medicine. Additionally, even when women have been included in clinical trials, results have rarely been disaggregated by sex, meaning there has been a lack of consideration as to how conditions and treatments can affect women differently. 

This has contributed to the gender health gap, which refers to disparities in health outcomes between sexes, and the gender data gap, which highlights the lack of sex-specific research and analysis. These gaps have profound consequences, ranging from misdiagnosis and ineffective treatments to increased adverse drug reactions among women. 

Closing these gaps requires systemic change in research design, regulatory frameworks, and funding priorities. In this article, which focuses on the UK, we explore the causes and implications of the gender health and data gaps and the steps that are being taken to close them.

Causes of the gender health gap 

The gender health gap has arisen for a number of different reasons, one of which is a historic lack of research and clinical trials either specifically focussed on women’s health issues, or including a representative sample of women. 

A 2025 study conducted by the MHRA and the University of Liverpool analysed the data on all 4,616 clinical trials submitted to the MHRA between 2019 and 2023. This analysis shows that there were 67% more male-only studies than female-only studies (making up 6.1% and 3.7% of all trials respectively). Further, reproductive and childbirth related trials constituted only 2.2% of all clinical trials submitted to the MHRA. 

Although 90% of clinical trials in the MHRA study included participants of both sexes, this figure does not tell the whole story. Women with child-bearing potential were only included in 33.1% of the trials. There was particular underrepresentation of pregnant women (only 1.1% of participants) and breastfeeding women (only 0.6% of participants). Therefore, merely including both sexes does not mean that the trial is representative of the overall population.

Additionally, unless researchers analyse and report results by sex, the results will not necessarily capture the differences between men and women. Where trials are not split up by sex, it can be impossible to know the extent to which sex disparities have an effect. 

The UK’s Health Research Authority confirms there is currently a lack of standardised guidance for researchers in the UK on how to adequately account for sex and gender differences in clinical studies. This contrasts with the approach in other areas of the world. For example, the EU’s Clinical Trials Regulation requires that the age and gender of subjects in clinical trials must be justified. The EMA is also publishing guidance aimed at closing the data gap, including a 2025 guideline for consultation on inclusion of pregnant and breastfeeding individuals in clinical trials. In the US, the National Institute of Health has required investigators to consider sex as a variable in vertebrate animal and human studies since 2016. The Canadian Institutes of Health Research (Canada’s federal funding agency for health research) expects all research applicants to adhere to policies on integrating sex and gender into health research. 

Consequences of the gender health gap

The consequences of the gender health gap are wide-reaching, spanning not only healthcare delivery and outcomes but also workforce composition and economic prosperity. A 2024 report by McKinsey states that closing the gender health gap could boost the global economy by an estimated $1tn annually by 2040, through improving the health outcomes of women and, in turn, optimising their economic participation.

On a national level, the Women’s Health Strategy for England policy paper published in August 2022 outlines a ten-year strategy for England to improve the health of women and girls. The report notes that while women typically live longer than men, women spend a greater proportion of their lives living with ill health and disability. One reason for this could be that women’s health research primarily focuses on diseases with high mortality such as ovarian, cervical and uterine cancer, rather than conditions affecting women’s day-to-day health such as polycystic ovary syndrome and endometriosis. 

The reluctance to include pregnant and breastfeeding women in clinical research has been shown to have tragic effects on women’s health outcomes. A BMJ study found that confusing messaging around vaccination during pregnancy was likely to have contributed to the deaths of 27 women in the UK during the pandemic. The EMA notes exclusion of these populations from clinical research has also resulted in product leaflets lacking details about the benefits and risks of a medicine during pregnancy and breastfeeding, contributing to the difficulty these women and their healthcare providers may face when making treatment decisions. 

Furthermore, women’s safety is impacted by a lack of clinical trials considering sex difference in drug responses. The 2024 McKinsey report notes that “since 2000, women in the US have reported adverse events from approved medicines 52% more frequently than men, and serious or fatal adverse events 36% more frequently.” In particular, women experience some asthma and cardiovascular disease treatments differently to men. As also highlighted by the 2024 McKinsey report, an analysis of the most used clinical interventions found that 64% of them disadvantaged women (because of limited access, lower efficacy or both). In comparison, this figure was only 10% for men. 

A 2022 paper on the results of a Phase III clinical trial for Alzheimer’s drug lecanemab reported a 27% reduction in cognitive decline among participants. While the trial did not analyse results by sex, data relating to subgroups contained in the paper’s supplementary materials suggested that for male participants the rate of slowing decline was actually 43% compared to only 12% for their female counterparts. As the trial was not designed to examine sex differences, it is unclear whether this discrepancy is in fact caused by underlying sex differences. However, these results highlight the gaps that can arise when clinical research does not account for sex differences.

Women’s health also impacts GDP and productivity. The effects of the gender health gap are most prevalent during women’s working years and this, in turn, is responsible for around 80% of the estimated impact on GDP. Addressing the gap can ensure women are able to work and be productive at work. For example, the 2024 McKinsey report highlights that approximately 80% of women experiencing menopause say it interferes with their lives, and that menopause has been linked to departing the workforce prematurely. The report concludes that addressing menopause and endometriosis alone could add up to $130bn to global GDP. 

Women’s personal finances are also affected by the gap. A 2024 report by Deloitte found that working women in the UK spend £1.5bn more per year on healthcare than men. On average, this equates to women’s out-of-pocket spending on healthcare being 50% more per year than that of men, with the most significant difference – around 250% – seen in fertility, menopause, and menstrual health spending. However, across areas affecting both sexes more generally, women still spent 25% more on general healthcare and private counselling or other mental health support than men and 10% more on medical diagnostics and wearables.

Solutions

Government and public body initiatives

There are currently no legal requirements in the UK to include women in clinical trials or disaggregate data by sex. This will continue even after the Medicines for Human Use (Clinical Trials) (Amendment) Regulations 2025 comes into force on 28 April 2026. This is despite the fact that the UK Government’s response to the 2022 consultation stated it would take forward a number of changes to support greater diversity in clinical trials.

However, governments and public bodies in the UK are putting in place guidelines and policies to address key causes of the health gap. The Medical Science Sex and Gender Equity (MESSAGE) project was set up in response to research showing that in 2021 no UK research funders or their major regulators had a policy requiring consideration of sex or gender of research participants or sex or gender disaggregation of data in analysis or reporting. The project designed a sex and gender policy framework and accompanying toolkit, which provides a best practice policy for UK research funders on accounting for sex and gender in biomedical, health and care research. While voluntary, as of December 2023, 29 organisations had published a statement of intent to support the project. These signatories from across the UK medical research community contribute £4.1bn per year to UK medical research. With influential organisations such as the Medical Research Council and the BMJ, as well as regulators including the MHRA, publicly supporting the initiative, it is hoped that further organisations will follow. 

Additionally, the UK Government announced in October 2025 that the Women’s Health Strategy will be renewed in 2026 to address specific barriers in access to healthcare. While there is no mention of how clinical trial disparities might be addressed, a commitment to remove barriers suggests implementing guidelines to R&D in the UK could form a central part of the strategy.

Funding opportunities

Outside government and regulator strategies, private funding provides grant opportunities for women’s health research. There are limited funding opportunities in the UK. However, at a global level, in August 2025, the Gates Foundation announced a $2.5bn investment to fund innovation in maternal, menstrual, gynaecological, and sexual health for women. Also, under Horizon Europe and its predecessor Horizon 2020, the EU invested over €2bn in projects focused on women’s health. Further, all research projects under Horizon Europe must integrate a gender dimension, unless the topic description explicitly specifies otherwise. 

AI and synthetic data

Despite these strategies taken by governments and regulators to combat the gender data and health gaps, there will inevitably be a delay between the implementation of these measures and the gaps closing. As biotech continues to transform with the use of AI, there is potential for AI and synthetic data to help to fill the gender data gap in the meantime. 

Synthetic data is artificially generated data that mimics statistical properties of real-world data, and can be used to increase diversity and representation in training datasets. Synthetic data can also mitigate bias from real-world data, for example by removing gender-based discrimination. 

In September 2024, the MHRA published its Data Strategy 2024-2027, which notes that while randomised controlled clinical trials are the gold standard for demonstrating efficacy, the data gathered is often not representative of the safety and efficacy of products across all potentially exposed patients. The Strategy discusses the importance of real-world data and notes the Clinical Practice Research Datalink (the MHRA’s RWD research service) has already been used to develop synthetic datasets. Therefore, the MHRA may be open to accepting use of synthetic data in the approval of products. 

There are however still risks associated with using synthetic data, as AI models trained on limited datasets can amplify data gaps or exhibit bias. For example, research from LSE found that some AI tools used in social care settings downplay women’s physical and mental conditions in comparison to men. To balance addressing gender data gaps with the need to ensure data is free from bias, it is clear that UK regulators will need to provide researchers and innovators with comprehensive guidance around the use of AI and synthetic data in healthcare and clinical trials. 

Final thoughts

Bridging the gender health and data gaps through inclusive research has the potential to transform women’s health and positively impact the economy (both in the UK and globally). While recent initiatives in the UK are a step in the right direction, continued progress depends on commitment from regulators and funders to prioritise gathering data specific to women’s health. Solutions such as the use of synthetic data could help bridge the gap until the effects of such initiatives become tangible, but will require clarity from the regulators.