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Why Scientists Wrongly Thought Periods Prevented Women from Thinking Clearly

A new study shows that hormones released during menstruation have no effect on women's cognitive abilities, challenging centuries of sexist assumptions.
Photo by Katarina Radovic via Stocksy

According to a new study, "period brain" isn't real. To put this in more sophisticated terms, researchers have found no evidence that cognitive function is impaired by hormonal changes during a woman's menstrual cycle.

The study, the biggest of its kind, was published in Frontiers in Behavioral Neuroscience last week; it followed 68 women over two menstrual cycles, and assessed memory, attention, cognitive bias, and hormone levels throughout both. In news may not surprise anyone with a period and a brain, the researchers concluded that, in general, a person's menstrual cycle has no effect on her ability to think clearly, make decisions, or concentrate on two things at once.


"The results aren't surprising," says Joan Chrisler, a psychology professor at Connecticut College and president of the Society for Menstrual Cycle Research. "We've known there's no effect for years."

For centuries, however, doctors have argued otherwise. The idea that menstruation makes women "crazy" has persisted since Ancient Greek times, when Hippocrates suggested women's wombs wandered around their abdomens, causing depression and madness.

Read more: The Racist and Sexist History of Keeping Birth Control Side Effects Secret

By the mid-1800s, doctors had started writing articles linking "insanity" to periods. In 1840, a French physician argued that menstruating women's "intellectual capacities were diminished, and they were subject to very peculiar caprices, to whims of character and taste," according to the historian Michael Stolberg. Similarly, in a presentation given to the British Gynecological Society in 1891, Dr. Robert Barnes described a certain patient of his, arguing that "there is an absolute coincidence between the menstrual period and the manifestation of insanity" in her case.

He continued: "The most frequent mental disturbance takes the form of modification of the natural disposition, which becomes quarrelsome and contradictory, and renders the patient a torment to the household."

A gynecologist examining his patient in the early 1800s. Image via Wikpedia

In 1931, Dr. Robert Frank published a paper entitled "The Hormonal Causes of Premenstrual Tension" in the Archives of Neurology & Psychiatry. In it, he argued that "premenstrual tension" was caused by a hormonal imbalance, and women suffer from "disturbances" like irritability and lack of concentration as a result. He recommended curing his imbalance by "expelling the excess hormones through urine and feces with the help of various diuretic substances." What followed was decades of research on the psychological effects of menstruation—but much of the methodology used in the countless studies on the subject is now seen as "problematic," the result of outdated research methods.


Even in recent years, there has been a host of scientific evidence that seems to back up the idea that a woman's menstrual cycle has an effect on her mental functions: Previous research has suggested that periods affect the area of the brain that controls memory, judgment, and attention; it's also been argued the changes in estrogen, progesterone, and testosterone can affect the levels of serotonin and dopamine in the body, which can result in anxious, irritable, and depressive moods.

But, as the recent study's lead author, Professor Brigitte Leeners, points out, many of these studies have scientific biases, false-positive findings, and inflated effect sizes, and their results are often hard to reproduce. According to Leeners, the majority of these "failed to find meaningful and consistent associations between hormones and cognitive functioning in women." For example, one paper used a sample of 16 women and only observed them during one menstrual cycle before coming to the conclusion that estrogen affects memory.

Notably, Leeners' research did not look at the disorder known as premenstrual dysphoric disorder (PMDD), a severe clinical mood disorder that consists of a number of affective, behavioral, and somatic symptoms that recur monthly during the menstrual cycle. It's been recognized as a disorder since 2013 in the DSM, and is said to affect between three and eight percent of women—although the research about this, too, is hotly contested.

It's been centuries since the days of the "wandering womb," but the logic that underlies that belief—that women's bodies and minds are fundamentally unruly or incomprehensible—has proved difficult to eradicate from our culture. Our persistent belief that hormonal changes associated with menstruation can affect women's ability to think clearly is rooted in "sexism and stereotypes about women," claims Chrisler of the Society for Menstrual Research.

Most scientists are men, she adds, and yet there is very little research about how their hormone cycle affects their cognitive functioning. "If you want to undercut women and make it seem like women don't belong in positions of power, then you have to say they're unstable, they can't be counted on to do the job right because they have hormonal cycles," she says.