Some Medication Is Still Only Tested On Male Mammals & Here's Why That's a Problem

by Emily Dixon

A new study has indicated that there are differences between the ‘male’ and ‘female’ immune systems — and yet medication for related diseases is not prescribed depending on sex assigned at birth (it should be noted that not all those with 'female' immune systems are women, and not all women have 'female' immune systems). What's more, some medication is still only tested on male mammals, as Wired reports, meaning that the resulting drugs might not be appropriate for patients assigned female at birth.

Dr. Susanne Wolf of the Max Delbrück Center for Molecular Medicine, Berlin, conducted a study into immune cells in the brain called microglia, in order to understand why male and female brains respond differently to diseases of the nervous system like Parkinson's disease or multiple sclerosis. She found that the microglia in female mice were different to those of male mice, telling Wired, "Male microglia are more numerous and larger, so arguably they react faster and stronger in the case of an attack. But on the other hand, they tend to overreact and wear themselves down more easily than female microglia."

Holger Kirk/Shutterstock

Why's this significant? Well, as Wired explains, drugs targeting the same disease haven’t been tested specifically for those assigned male and female at birth. What's more, drugs are often tested solely on male mammals, typically in order to sidestep female hormonal cycles. That's a particular problem in neuroscience — according to Wired, a 2010 study indicated that "single-sex studies of male animals outnumbered those of females 5.5 to 1 in that field."

Some research organisations are addressing this inequality, as the magazine observes. "In 2014, the National Institutes of Health (NIH) passed a rule that obligated researchers to have a valid explanation when using single-sex animal models," Wired explains. "The European Commission similarly started the Horizon 2020 campaign — a research and innovation program stretching over seven years with the objective, among others, of including gender differences in research."

And Professor Gina Rippon of the Aston Brain Centre observed another reason scientists might hesitate to factor the sex of test subjects into their work. "One of the concerns is that quite often people jump to interpretations of sex differences to prove that there are biological differences between men and women," Rippon told Wired. Still, Dr. Suzanne Wolf told the publication, "If you are only using male models to research and then develop drugs to treat immune diseases, then clearly it will have an impact on the way we treat [patients assigned female at birth] because you will not have been producing drugs that are appropriate for everybody."