Now, another old wives’ tale has been debunked. Next time someone implies you might be off your mental game because it’s your time of the month, hit ‘em with the results of a new meta-analysis of more than 100 studies, which found zero evidence for the idea that cognitive abilities change across the menstrual cycle.

“Women’s cognitive performance throughout the menstrual cycle has been the topic of much writing and speculation,” begins the paper. “Menstruation in particular is often treated like a disease, impairing women’s ability to function.”

It’s true both in the messages we receive and the ones we send out – but what does the research say? A cursory glance at the literature might suggest the jury’s still out: some investigations have supported the idea, only to later be disputed or debunked; some imaging studies have found no cognitive differences across the menstrual cycle, and some self-reporting has claimed the exact opposite.

Luckily, science has a powerful tool to make sense of this kind of confusion: the meta-analysis. By combining the results of many different studies, researchers can come to a much more robust conclusion than any of the individual papers could reach on its own.

Doing so in this case, though, wasn’t easy. “There are methodological concerns that make it challenging to evaluate the conflicting evidence in the literature,” the researchers explain. “A long standing limitation in this area of research is that sample sizes are typically small, with studies sometimes reporting fewer than 10 participants. Other challenges include inconsistent definition of cycle phases into date ranges and reliance on self-reports of cycle phase that are not reliable indicators of endocrine and other physiological changes.” 

An effective meta-analysis, then, would mean controlling for all of these limitations – but once they pulled it off, the results were pretty clear.

“We find little consistent evidence that women’s cognitive ability changes across the menstrual cycle when examining numerous domains of cognitive performance,” the study concludes. That includes no significant changes in attention, creativity, executive function, intelligence, and motor function at all – and while some significant differences were found in participants’ memory, spatial ability, and verbal ability, all were concluded to be non-robust, meaning they’re likely quite specific to the particular groups studied rather than a general population.

As the researchers themselves note, this might be surprising. After all, “levels of estrogen, progesterone, and luteinizing hormone fluctuate in a well-understood manner” throughout the menstrual cycle, “and receptors for estrogen in particular are present in many parts of the body, including the central nervous system and the brain. Moreover, both brain structure and functional activation patterns change across the cycle, which suggests fluctuations in ability.” 

That they found no evidence of cognitive changes, then, points to one of three possibilities: either the physiological changes aren’t big enough to make a difference to cognitive ability; the differences between individuals is greater than the differences across one person’s cycle; or… some secret third thing, “not yet understood,” the team writes.

Of course, that last option might seem like a cop-out – but the truth is, there’s still an embarrassing number of questions around menstruation for which the answer is “not yet understood”. It’s a big enough problem to have impacted the meta-analysis, with the authors pointing out the need for more research in certain areas, more standardization across the board, and a wider and more diverse sample pool.

Nevertheless, with the information we do have, the story seems pretty clear: your period does not affect your cognitive ability in any significant way. 

“One can never prove a null hypothesis,” the authors caution – but “an effect would need to be very small if it does exist based on the methods used in existing work.”

The study is published in the journal PLOS One.