There's no evidence that a woman's cognitive abilities change during her menstrual cycle, a meta-analysis of over 100 studies on the topic has found.
While serious conditions like PMDD, dysmenorrhea, and endometriosis can certainly be disabling – especially when social resources are denied to those affected – it turns out run-of-the-mill menstruation just doesn't live up to its brain-scrambling reputation.
This area of research has long been plagued by small sample sizes, limited measures of cognition, and of course, the fact that women's bodies have been sidelined for most of scientific history.
And while subjective and cultural ideas around 'period brain' concern half the population, the scientific basis is lacking.
Organizational behaviorist Daisung Jang, from the University of Melbourne, led a meta-analysis reviewing 102 peer-reviewed scientific papers that had assessed various measures of cognition throughout the human menstrual cycle.
The review collated data from nearly 4,000 menstruating women whose cognitive performance was tested throughout their cycles, in terms of attention, creativity, executive function, intelligence, memory, motor function, spatial ability, and verbal ability.
The papers had to provide the number of women who were measured for cognitive ability, based on specific days of the menstrual cycle, in order to qualify.
The study excluded papers with variables that may confound cognitive results, based on keywords like "pregnancy", "infection", "disorder", and " cancer." So the results apply only to more 'baseline' experiences of menstruation.
The study data was limited to females, so the results may not apply to people of diverse genders. It also included only papers published in English.
It's well known that hormones like estrogen, progesterone, and luteinizing hormone rise and fall at various points through the cycle, and these changes, particularly when it comes to estrogen, are felt by receptors throughout the body, including the brain.
And yet, the differences Jang's team found in women's cognitive performance across the menstrual cycle were so small and inconsistent they were deemed insignificant: there is no evidence, here, that female brain power is at the whim of the monthlies.
"This lack of findings is somewhat surprising given the numerous documented physiological changes that occur across the cycle," the authors write.
These hormonal tides may be so subtle that they have little effect on what's going on upstairs, or perhaps, as the authors suggest, women are able to compensate for these changes in some ways not yet understood.
Throughout history, women have been held back by the assumption that menstrual cycles impair their cognitive function. For some, it may be hard to imagine going about your day like everything is fine while secretly bleeding and wincing in pain. Or maintaining an even keel while your hormones do a complete do-si-do on a fortnightly basis.
The results also don't rule out the possibility that physical changes in the brain, as a result of menstruation, may have a greater effect on cognition for some women than others, for reasons not addressed in this study. This would blur any trends that might be lurking.
Previous studies have found little difference in the hormones of menstruating people with and without premenstrual stress symptoms, for instance, suggesting that PMS is more to do with how each person's body responds to the hormones, rather than their levels generally.
"Physiology does not appear to be destiny with respect to cognitive ability," the authors write.
"This result has implications for addressing misconceptions and myths as well as addressing discriminatory practices, as we found no scientific basis for doubting women's ability to think because of their menstrual cycle."
This research was published in PLOS One.