Psychology and the Pill
Hormonal contraception may affect stress, choice of partners and more, Sarah Hill finds.
It was a throwaway line, a footnote mentioned in passing by a speaker at a psychology conference:
Women on the birth control pill are missing a key feature of their stress response.
For Sarah Hill, professor of psychology at TCU, the simple statement was the equivalent of a fire alarm.
Hill had already been smelling smoke over the effects of hormonal birth control on women. Two years earlier, she had noticed striking changes when she went off the birth control pill after a decade of taking it.
“I felt like I woke up from a nap I didn’t know I was taking,” she said. “I just felt so much more vibrant, energetic and alive than I had in a really long time.”
A year after Hill’s awakening, a colleague recommended a research paper showing differences in the relationship satisfaction and divorce rates between women who take the birth control pill and those who do not.
“It was intriguing to me,” Hill said, “that this sort of medication that we take simply to prevent pregnancy might have these really cascading effects.”
When Hill heard about the changes in stress response, ideas that had been smoldering in her mind about this contraception method used by millions of women sparked into flame. “In that moment,” she said, “I recognized and appreciated that the birth control pill is probably influencing everything.”
That revelation needed further research, which Hill compiled and shared in her book, This Is Your Brain on Birth Control: The Surprising Science of Women, Hormones, and the Law of Unintended Consequences (Avery, 2019).
According to data from the Centers for Disease Control and Prevention, 12.6 percent of reproductive-age women in the U.S. use birth control pills; an additional 10.3 percent use long-acting hormonal contraception such as an intrauterine device (IUD) or implant.
Because birth control is a complex and controversial subject, Hill started the book with a disclaimer that she does not have an agenda.
“This [birth control] is a personal decision,” she wrote. “This book is for each woman to be able to have the information that she needs to be able to make the most informed decisions moving forward.”
Hill approached the book and her research on women’s health and relationships through the lens of evolutionary psychology. Her academic specialty examines the adaptations — in brain structure, cognition and behavior — that promote survival and reproduction.
“I felt like I woke up from a nap I didn’t know I was taking. I just felt so much more vibrant, energetic and alive than I had in a really long time.”
“One of the things that is really important to me as someone who teaches evolutionary psychology is teaching people how they work,” Hill said. “How does your brain work? How does your body work? What was it designed for?”
The entire female body, not just a group of specific organs, was designed to reproduce. Receptors for the sex hormones estrogen and progesterone exist throughout the body and especially in the brain. When women begin taking hormonal birth control, the synthetic hormones are picked up by all of those receptors.
But the messages these artificial hormones broadcast throughout the body don’t necessarily mimic those of their natural counterparts. Birth control “is going to rewrite all systems from top to bottom,” she said, “including the brain.”
Sex Kitten/Mom Jeans
Women’s monthly cycles occur in two phases. During the follicular phase, when women are most fertile, estrogen dominates. “Estrogen is the flirtatious sex kitten of women’s hormones,” Hill wrote.
The chemical prompts the release of an egg and formation of the uterine lining; it also influences women’s psychology and behavior in ways that help facilitate conception. Research shows that when women are at high fertility, they have increased sexual desire, feel sexier, put more effort into their appearance and engage in sex more frequently. They’re also more attracted to men with certain physical traits, such as a symmetrical physique and deep voice, that telegraph desirable genes. In turn, men find the scent and face of a woman at high fertility to be more attractive.
“The idea that women might choose different partners when they are on the pill than when they are off it suggests that the pill may have rippling effects on the quality and dynamics of women’s long-term relations — maybe even the risk of divorce or infidelity.”
During women’s other menstrual phase, progesterone surges as the body anticipates the implantation of a fertilized egg. “Progesterone is more of the mom jeans, Earth mother hormone,” Hill wrote. “When progesterone is on the scene, women tend to feel hungrier, sleepier and more relaxed than they do at other points in their cycle. It makes women feel like doing the kinds of things that help get their body ready for the possibility of needing to grow another human being in the not-too-distant future.”
In contrast to the naturally occurring variations in hormone levels each month, most birth control pills administer a uniform daily dose of synthetic estrogen and progestin, a synthetic progesterone often derived from testosterone. This “hormonal déjà vu,” as Hill put it, prevents ovulation by making the brain think that a woman’s cycle is parked in the luteal, mom jeans phase.
No ovulation means no pregnancy, which is why most women take birth control. But research reveals other effects of static hormone levels. Pill-taking women experience lower sexual desire and show a consistent preference for men with less masculine faces and voices, the same preference that naturally cycling women have in their luteal phase, the book says. In fact, one study shows that the pill may blunt women’s sense of smell, hampering their ability to sniff out men with markers of desirable genes.
“The idea that women might choose different partners when they are on the pill than when they are off it suggests that the pill may have rippling effects on the quality and dynamics of women’s long-term relations — maybe even the risk of divorce or infidelity,” Hill wrote.
One survey indicated that women on the pill had lower sexual satisfaction but higher satisfaction with their partners’ intelligence and ability to provide financially, qualities that might increase a woman’s sense of security during pregnancy, the book says. These women were significantly less likely to divorce. Another study found that when women went off the pill, their marital satisfaction changed, but whether it was a positive or negative change depended on how attractive their husbands were — a mate selection factor the pill may have influenced to begin with.
Such societal ripple effects represent the unintended consequences that Hill referred to in her book’s subtitle.
“Dr. Hill is uniquely positioned in her perspective on birth control,” said Jolene Brighten, author of Beyond the Pill (HarperOne, 2019). “She shows how it impacts not only the individual but society as a whole, for better or for worse.”
Acknowledging that birth control pills could influence sexual desire and behavior is no intellectual stretch. But what do those pills have to do with a woman’s stress response?
The answer is cortisol. When a person experiences stress, cortisol is released through the hypothalamic-pituitary-adrenal, or HPA, axis. The brain signals the pituitary gland to instruct the adrenal gland to release the hormone cortisol into the bloodstream.
“Cortisol allows us to be able to learn from stressful situations and then be able to adapt better to stressful situations in the future,” Hill said.
Research shows that women on the pill have a blunted cortisol response — and in some cases, none at all. What does this mean? They still feel stressed or anxious; that’s a response of the body’s sympathetic nervous system, Hill said. But the hormonal axis mixes up the signals and goes haywire. The adrenal glands produce such an excess of cortisol that the entire system turns off, she said. This pattern “looks a lot like what you see in people who’ve experienced chronic trauma or chronic stress.”
When cortisol chronically floods the body, it triggers a cascade of detrimental effects. Excess stress hormone increases the level of sugar and fat in the bloodstream, which can raise the risk of diabetes, weight gain and heart disease. Too much cortisol can shrink the hippocampus, a part of the brain associated with emotions, learning and long-term memory. Reduced hippocampal volume is linked to emotional and cognitive problems and is a hallmark of Alzheimer’s disease, the book says.
“There’s no research linking pill-taking and the risk for Alzheimer’s,” Hill said, “but it certainly raises the question: Are these things related?”
Once the stress-response axis shuts down, it deprives the body of the necessary cortisol not just in times of stress but in times of attraction, too, Hill said. Cortisol signals to the brain that something is significant, whether it’s a person who could be a potential mate or an emotionally meaningful event. In its absence, women’s ability to cope, learn, adapt and connect might suffer.
“The pill, by taking away the ability to biologically absorb meaning from their environments,” Hill wrote, “may make women feel emptier than they would without it.”
Listen to the TCU Magazine Podcast interview with Sarah Hill:
A feeling of emptiness can be a red flag for a more serious problem: depression. As Hill explained in the book, researchers cross-referenced two of Denmark’s national health registries: one recording all diagnosed psychiatric diseases and another tracking all prescriptions filled. They followed the charts of more than 1 million women over a 14-year period. They found that women on hormonal contraceptives were 50 percent more likely to be diagnosed with depression than women who were not. Women using non-oral contraceptive methods (patch, hormonal IUD and vaginal ring) had an even higher risk of depression.
The data was particularly alarming on females ages 15 to 19, who might take hormonal contraception to clear acne, regulate their periods or reduce the frequency of migraines rather than for pregnancy prevention. With some birth control pill formulations, the risk of depression was up to 160 percent higher compared with females not on hormonal contraception in this age group.
The same researchers also documented a staggering increase in suicide risk for females 15 to 19 who were on hormonal contraception. They were twice as likely to have attempted suicide and three times more likely to have died by suicide than those not on hormonal contraception.
“When you change a woman’s profile of sex hormones during this time, there is a very real, and I would argue an unavoidable, consequence that you’re going to be altering the developmental trajectory of the brain.”
Why is this age group particularly at risk? “Adolescence is a time where, in addition to the body undergoing a variety of developmental changes, the brain is, too. Sex hormones are what’s calling the shots,” Hill said. “When you change a woman’s profile of sex hormones during this time, there is a very real, and I would argue an unavoidable, consequence that you’re going to be altering the developmental trajectory of the brain.”
The Danish data resonates with Dr. Louann Brizendine, author of The Female Brain (Morgan Road Books, 2006) and a professor at the Weill Institute for Neurosciences at the University of California, San Francisco.
“About 50 percent of women who go on the pill will tell their OB-GYN that it makes them depressed or not feel good in some way,” Brizendine said. Hill’s book “sounds an alarm for us to do a deeper dive into what is going on here and to individualize treatment.”
A deeper dive is exactly what Hill hopes patients and clinicians will take as they consider contraceptive options. She encouraged women using hormonal birth control to keep a journal, tracking physical or emotional changes they experience and sharing those details with their doctor.
“Ask yourself, How is your mental health? How is your level of vibrancy? Are you seeing any problems with learning and memory?” Hill said. “This can help women identify whether or not a birth control pill is working for them and, if not, help them troubleshoot and find either a different pill that is going to allow them to feel more at home in their own bodies or try something else altogether.”
As Hill frequently reminds her readers, contraceptive science is still evolving.
“The issue of birth control for women is not solved yet,” she wrote in her conclusion. “It’s time for all of us to join together to ask science for some new choices and for more information about what happens to us with the choices we have. … This will require nothing less than a complete paradigm shift in how we view our brains, our hormones and ourselves.”