How we perceive the world, form memories, and experience satisfaction fundamentally define the way we live and who we are. Recent science and widespread firsthand accounts now show that hormonal contraception, including the birth control pill, profoundly affects these domains by altering the structure of the brain and our neurochemistry.

Hormonal contraception (HC) has long been regarded as a relatively safe and effective option for women seeking to prevent pregnancy since the 1960s. It has also been prescribed for a wide range of conditions ranging from acne to polycystic ovarian syndrome.

About 80 percent of women will end up taking some kind of hormonal contraception at some point in their lives—most commonly in the form of the birth control pill. But, recent science is showing that it can blunt women’s stress response, affect how they form memories, and even change who they’re attracted to.

How the Pill and Other Hormonal Contraceptions Work

In a naturally cycling woman, the first two weeks of the ovarian cycle is called the follicular phase, which ends with a sharp increase in estrogen—which is not just one—but a group of sex hormones. Around day 14, the ovary releases an egg, known as ovulation.

The next phase is known as the luteal phase and is marked by a rise in the hormone progesterone. When there is no fertilization, menstruation occurs and the two hormones return to baseline levels. The cycle begins again, typically lasting roughly 28 days in total.

Hormonal contraception works by continually releasing artificial hormones into the body, either in pill form, injection, or via an intrauterine device (IUD). HCs release synthetic estrogen, synthetic progesterone, or a combination of the two. This causes the ovaries to stop releasing natural hormones. Hormone levels remain flat, rather than rising and falling as in the natural cycle.

Attraction, Perception, and Memory

Jasmyne Theodora, a content creator who focuses on traditional femininity, began using the Mirena IUD when she was 17. Now 23, she explained how she began using it because her cycle was irregular and her periods were difficult. Though an IUD is hormonal, it does not have a control week like the birth control pill, so she lost her period completely.

But, as she began to learn how the cycle is a strong indicator of overall health, she questioned her decision to use HC and began her research.

“Instead of completely stopping my period, I wanted to get to the root cause of why it was so uncomfortable because it really should not be a horrible time for women,” Theodora told The Epoch Times.

She produced a detailed video essay that spotlights the effects of hormonal contraception, including research into how it affects attraction. These studies built upon earlier research that found the varying hormone profile throughout the ovarian cycle produces fluctuations in sexual preference among women, according to a 2008 study published in Hormones and Behavior. Researchers found that as estrogen spiked in the cycle, women preferred the faces of men with higher levels of testosterone.

One study in Psychoneuroendocrinology from 2013 found that, as compared with naturally cycling women, starting the birth control pill decreased women’s preference for male facial masculinity. Women who chose partners while on the pill experienced lower sexual satisfaction and were more likely to initiate separation, according to a study published in the Royal Society’s Proceedings B in 2011. But, they also tended to be more satisfied by their partner’s ability to materially provide, had longer relationships, and were, overall, less likely to separate. Also, a 2008 study from the same journal found that pill-taking women were more likely to choose partners that smelled genetically similar to them.

Theodora shared her own change in partner preference.

“When I was on the [IUD], the men I dated were actually mostly shorter than me. They were very agreeable, very nice guys,” she said. “When I got off the [IUD], I was attracted to a completely different kind of man,” she said.

Before the IUD, she said she tended to be attracted to taller, more masculine men. After she stopped in 2021, she found herself returning to this preference in dating and marrying her husband.

Theodora also noticed that after she stopped HC, she felt more exuberant.

“I just felt I had a bit more of a verve for life. I didn’t realize that I felt kind of ‘blah’ until I got off of it … I just had a bit more enthusiasm for everything.”

Theodora credited this renewed vitality to the rebalancing of her hypothalamic-pituitary-adrenal (HPA) axis. When we encounter stress, this system activates and the well-known hormone, cortisol, is released. Research published in Psychoneuroendocrinology in 1995 has shown that oral contraceptive users showed a blunted cortisol response to stressors. Since then, this pattern of a diminished cortisol response has been repeated over several studies.

From a chemical lens, this lack of cortisol response might be interpreted as lessened stress on a subject, which some may even consider a positive outcome, but that likely isn’t the case.

As Sarah E. Hill, an award-winning research psychologist and professor with expertise in women, health, and sexual psychology and the author of the 2019 This Is Your Brain On Birth Control, writes:

“… The pill-taking women’s pattern of HPA-axis function looks suspiciously similar to that of someone who has experienced chronic stress, suggesting that the pill might actually cause the HPA axis to go into overdrive, requiring it to take coordinated action to blunt itself.”

In considering four biomarkers of chronic stress exposure, researchers found that HC users displayed all four, including reduced volume of the hippocampus, a major part of the brain involved in memory and spatial navigation, as published in Nature’s Scientific Reports in 2017.

Stress tends to carry negative connotations, but it actually plays a vital role in helping us overcome obstacles, according to a 2012 study in the Journal of Neuroscience; identifying social opportunities; as shown by a study published in 2011 in Neuroscience & Biobehavioral Reviews; and even promoting sexual attraction, according to a study published in Hormones and Behavior in 2019.

Without an active stress response, Hill writes, “it might lead women’s brains to believe that they are living in an unstimulating world that lacks the promise of exciting new possibilities and challenges.” Interestingly, a 2020 study from Hormones and Behavior found that HC users displayed less perseverance in both simple and cognitively challenging tasks.

The stress response is also key to memory. It can enhance it, as published in PNAS in 2009—or hinder it—according to a 2006 study in Annals of the New York Academy of Sciences. Building off HC’s impact on the stress response, coupled with evidence published in Psychoneuroendocrinology in 2008 that sex/stress hormone interactions can affect emotional memory, researchers sought to test this further. They compared how naturally cycling women differed from HC-using women in remembering a story, in a 2011 study published in Neurobiology of Learning and Memory.

They showed both groups either an emotionally arousing story or a more neutral story with similar content. Naturally cycling women showed greater recall of details, but not of the gist of the emotional story. HC-using women were inverted, showing great recall of the gist, but not the details.

“These findings suggest that the use of hormonal contraception alters memory for an emotional event, perhaps by altering sex/stress hormone interactions in memory formation,” the study authors conclude.

A Tale of 2 Estrogens

Dr. Felice Gersh, an OB-GYN practicing integrative medicine based in California, described the synthetic hormones used in HCs as “endocrine disruptors,” whereas natural estrogen and progesterone are actually neuroprotective.

“When you take birth control pill estrogen, that is really an endocrine disruptor,” she told The Epoch Times. “They’re chemicals. They’re never naturally found in a human body.”

Three main estrogens operate in the body: estrone, estradiol, and estriol. The most important and prevalent is estradiol. It is what HC mimics with the use of synthetic ethinyl estradiol.

In the brain, the hypothalamus—responsible for much of the body’s automatic functions—and the limbic system—involved in emotion, reproduction, and survival—are more populated with alpha estrogen receptors, which estrone binds to.

In the cerebral cortex—the outer part of the brain that contributes to cognition, memory, and consciousness—there are more beta estrogen receptors, which estriol binds to. The cortex is usually viewed as the newest part of the brain, involved in higher-order functioning.

Activation of one receptor type influences other receptors, Dr. Gersh said, i.e., increased alpha activity will reduce beta activity. But, natural estradiol can convert into either estrone or estriol, and it has a more balanced effect on all estrogen receptors.

However, she said, ethinyl estradiol, the estrogen used in HC, is heavily converted into estrone in the body. She speculates that this can produce an uptick in alpha activity, potentially depriving the cerebral cortex of beta receptor activation.

“Since it’s not really working as much on the cerebral cortex, there is the worry in my mind that it’s going to be basically creating a deficiency state in the brain,” Dr. Gersh said, adding the caveat that we don’t yet have hard evidence for this.

Toward New Ways to Manage Fertility

There is no doubt that hormonal contraception has produced a range of benefits for women since its widespread use. It can help women regulate hormonal issues in cases where other treatments fail. It can potentially reduce the risk of certain cancers. And, it affords women a greater degree of freedom over their fertility and reproduction.

However, when it was initially formulated 70 years ago, we knew little about how hormones operate in the body, Dr. Gersh stressed.

“I’m not in favor of uncontrolled fertility, but we have to be honest about what we’re doing,” she said. “And, if we don’t acknowledge that this is happening, then we’ll never come up with better ways to control fertility.”

Theodora, a newly minted mother, acknowledged the benefits of HCs but also said if she knew then what she knows now, she would likely not have started using it.

“You are your hormones. Your hormones make up who you are to a very large extent,” she said. “When you take birth control, it affects your hormones … so significantly that it definitely can change who you are.”