Understanding what these influences are, their full range of impact and how to change and manage them is critical to the health of women. But until recently, most of it has been ignored and gone unstudied, Hill writes in This Is Your Brain on Birth Control: The Surprising Science of Women, Hormones, and the Law of Unintended Consequences.
“This book, hopefully, it's going to give women a lot of self-understanding, and also really an appreciation for how amazingly complex and well functioning our bodies really are,” Hill said.
She wants women to use the book to understand their own bodies and to be able to make well-informed decisions about their health. Women need to know there are a lot of options out there, and Hill hopes the book will offer them a better way to articulate why one kind of birth control isn’t working and how another one might be a better fit.
Through a humorous and bizarre, example-infused recounting of her own research and an extensive literature review, Hill lays out how, in addition to preventing unwanted pregnancies, hormone-based birth control can influence a woman’s choice of partner, physical appeal to potential partners, sex drive, stress response and mental health.
And yet, because the available birth control is overwhelmingly for women, and pregnancy primarily impacts women’s lives, women have put up with the known, and unknown, side effects for years, because the trade-off is worth it. And the world has been a better place because of this, Hill said.
“If you think about all the amazing people you've known in your life who've been women … And these women, a lot of them would have had their voices silenced and their contributions minimized because they would be dealing with pregnancies that they didn't want,” Hill said. “And so we have opened up, you know, as people, all of this new brain power by allowing women to regulate their fertility.”
Since an unintended pregnancy makes a much bigger impact on a woman’s life than on a man’s, women also carry most of the burden of preventing those pregnancies. Most available birth control options are hormone-based. But hormones are everywhere in the body, and so mucking around with hormones to prevent pregnancy invariably, if unintentionally, changes processes throughout the body.
Hormones influence pretty much everything in the body. Both men and women have hormones that direct the body’s major functions. In the book, Hill describes them as a comprehensive loudspeaker system that tells the rest of the body how to act. Hormones travel though the bloodstream and are picked up by, and interact with, cells that have matching hormone receptors.
If you break down what it means to be a human being to its base level, that essence consists of a series of brain signals and hormones — stress hormones, sex hormones, sleep hormones, etc., she said. So the idea that a drug can go in and simply influence whether a woman gets pregnant, without reaching into the other parts of the body, is completely unrealistic. But so is the idea that hormones are something to be feared or degraded, Hill said.
“The idea that being ‘hormonal’ is bad, is also something that's crazy and not backed up in science. If we didn't have our hormones, we wouldn't sleep, we wouldn't eat, we wouldn't have sex, we wouldn't be attracted to anybody,” Hill said. “I mean, we would just be these weird robots that wouldn't know what to do with themselves.”"If we didn't have our hormones, we wouldn't sleep, we wouldn't eat, we wouldn't have sex, we wouldn't be attracted to anybody. I mean, we would just be these weird robots that wouldn't know what to do with themselves.” — Sarah Hill
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Unlike men’s hormones, which truly can change at the sight of a gun, a sports event, a pretty woman and in response to many other situations, women’s sex hormones rise and fall in a predictable pattern each month. In the first half of a woman’s cycle, the hormone estrogen is dominant as a woman’s body prepares for a potential pregnancy and the release of an egg during ovulation. In the second half of the cycle, the hormone progesterone takes over and prepares the body for the pregnancy that could be about to start, if that egg has been fertilized.
Birth control tricks a woman’s body into thinking it is in this second part of the cycle all month long so that it doesn't prepare for or release the egg, whose presence is required for pregnancy to occur, Hill explains in the book.
Studies have shown that women on birth control are more likely to choose men for their financial stability and intelligence than for physical attractiveness, whereas women who are not taking hormones at the time they get into a relationship tend to choose more on physical attributes and attraction. When women who have taken hormonal birth control for years go off of it, some of them feel differently about their partners than they did while they were on the pill.
In fact, Hill herself began to wonder about the effects of the pill when she went off it. After having her two children, she stopped birth control after taking it for more than a decade. She describes the experience as something akin to waking up. Slowly, she became interested in things she thought she had outgrown. She began to notice her husband more, she enjoyed exercising and cooking, she started listening to music again. It was as though her life, which had been muted on the pill, was suddenly full volume again.
Then, at a conference in about 2014, a colleague was presenting the methods section of a study of his about early-childhood stress. He casually mentioned that he didn’t include women in the study, because most women are on hormone-based birth control and when they are, they do not exhibit a cortisol reaction to stress. Hill was surprised by this and wanted to know more. It turns out that women who take hormone-based birth control have roughly the same cortisol response as veterans suffering from severe PTSD.
This doesn’t mean that women taking birth control don’t get stressed, but rather that they aren’t necessarily as equipped to handle it as women not taking artificial hormones and that in lab tests, their cortisol responses barely register.
But that dampened cortisol response only matters if it is making a noticeable impact on a woman’s life. Many women take birth control for years with no problems, and they should not worry, Hill said.
Some women who take the pill experience psychological changes, mood and life-satisfaction shifts and depression. Different pills have different kinds and levels of hormones in them and will interact with a woman’s physiology differently. Knowing what these differences mean and that mood changes and other common effects, like a total disinterest in sex, are not normal is important, Hill said.
In the book she provides a chart of all the kinds of birth control pills, and the hormone types and levels in them.
Hill is most wary of the effects of hormonal birth control on the brains of girls under the age of 19. Although we know that human beings’ brains continue to develop into our mid-20s, the time before a woman turns 19 is especially critical. Because hormonal birth control directly affects brain function, it follows that it might have a bigger long-term impact on developing brains. However, Hill said, the research hasn’t been done on this and it needs to be.
But Hill is also clear that if the options have not changed by the time her own daughter becomes sexually active, hormonal birth control may still be the best way to prevent an unwanted pregnancy.
Deciding to go on birth control is all about evaluating the risk-to-reward ratio. If her own daughter were not regularly using condoms and unable to tolerate other non-hormonal birth control options, she would choose to put her daughter on the pill. She would not, though, want to put her daughter on birth control simply to manage her period or acne breakouts, as is a common practice.
While all of this might sound kind of scary, it’s important to note that many women take birth control for years and are perfectly fine, Hill said. So, the first thing to do with all of this information is to take a deep breath. Be patient with yourself. Know the facts. Pay attention to your body. Keep a journal about how you act and feel on a day-to-day basis. And if it feels as though your new birth control is affecting your mind, talk to your doctor and try another option, Hill suggests.
There is a lot more research that needs to be done to understand what happens to women’s brains on birth control, to try to improve the situation and to explore other options, Hill said.
For many women, hormonal birth control is still the best and necessary option. In person and in the book, Hill is careful to emphasize that she is not making recommendations for specific people. For women, parents of and partners to women, the book should empower better choices, not instill fear.
“Information is power," she said. "Use it to make your own life better. You're the expert in you; do you."
