The complexity of female sex hormones calls for more science, not less

In 1977, the US Food and Drug Administration (FDA) imposed a ban on women of childbearing age being included in early drug trials – even if they used contraception or had vasectomised partners. This was a reaction to harms caused by drugs like thalidomide, which can lead to birth defects.

Even before the ban (which was lifted for non-pregnant women in 1993) women and female animals were regularly excluded from research – their fluctuating hormone levels seen as complicated noise. Female data is still often extrapolated from research on male animals.

The cost of this lack of inclusion is clear: it has skewed our understanding of health and disease and left us woefully ill-informed about conditions that predominantly affect women.

A classic example of this came in 2013, when more than 20 years after the sleep aid zolpidem was approved, the FDA halved the recommended dose for women as evidence emerged they experienced more daytime drowsiness than men, leading to more driving accidents.

Progress is being made. Increasingly, researchers are considering sex as an important biological variable, leading to recent discoveries that women are twice as likely as men to be diagnosed with depression, for instance, and that they get cardiovascular disease at lower levels of blood pressure.

But there is still work to do. While many funders now insist that research includes two sexes, conditions that mostly affect women – such as migraine, endometriosis and premenstrual dysphoric disorder (see “Surprising insights into the causes of PMDD promise better treatments”) – continue to attract much less funding in proportion to their burden on the population. That hormones and their actions make research more complex should be a reason to invest more, not less.

Had these conditions predominantly affected men, there would no doubt be more treatments available. The stories of people living with PMDD should be read as a stark reminder of the cost of this inequality.