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There is a lot about birth control we still don’t really understand. Does it clear up our acne? Does it make us gain weight? Could it lead to depression? Could it solve PMS?

Hormonal birth control works by releasing artificial versions of our sex hormones — estrogen and progesterone — tricking our brain into thinking our body is at a point in the menstrual cycle when the ovaries don’t need to release an egg. These artificial hormones travel through our bloodstream, reaching every part of our bodies, including our brains. That is where things get interesting.

In “This Is Your Brain on Birth Control,” released today, Sarah Hill, a professor of psychology at Texas Christian University (TCU), tries to explain exactly how women’s brains and behaviors might change because of hormonal birth control, including the pill, the IUD, the patch, and the arm implant. (All these different varieties work by changing the hormonal message to the brain, Hill says, so they can have similar side effects.)

It’s a difficult task. While millions of women in the United States regularly use hormonal birth control, there is an astonishing lack of definitive research on its side-effects. The research that does exist is largely inconclusive, or contradicts a previous study, or fails to examine the particular effects of the dozens of individual strains of hormonal birth control, each with its own distinct hormonal recipe. Birth control seems to negatively affect mood for some people, for example, and positively affect mood for others.

Hill ends many of her chapters with a similar disclaimer:

“The following section is super speculative.”

“It will probably be years before we have definitive answers.”

“We may never know.”

Still, Hill says, it’s important for women to be able to make choices about birth control “with their eyes wide open.” We should know about the research that exists, she says — at least enough to ask our doctors the right questions.

“If we don’t understand ourselves, then we end up having to rely on our doctors to tell us what to do,” says Hill. “And that is a completely anti-feminist position.”

(Courtesy of Penguin Random House)
(Courtesy of Penguin Random House)

Caroline Kitchener: You start this book by explicitly saying, “I do not have an agenda.” Why did you decide to start things off that way?

Sarah Hill: I did that very intentionally. Women’s hormones, and especially their involvement in the brain, is a hugely polarizing issue. For a really long time we were taught that, as women, our best defense against sexism is to simply pretend like our hormones don’t influence our behavior. But if we ignore the role that hormones play in shaping who we are, that ends up being really bad for women. It decreases women’s ability to understand ourselves.

People are also, understandably, very protective of the birth control pill. I can’t think of anything that has done more to better women’s lives than the pill — maybe safe, legalized abortions. But both those things have the same effect: allowing women to make plans, invest in their education, invest in building their careers.

CK: Do you think people will be skeptical because you work at TCU, a Christian University?

SH: It’s definitely crossed my mind. Surely, someone who didn’t read the book will write something, somewhere that will say I have a religious agenda. “Die-hard Christian professor” … who, it turns out, is also an atheist and writes extensively about her lack of religious scruples in the book.

CK: You write about your own personal experience with birth control in the book. How did going off the pill change things for you?

SH: I felt like I woke up from a nap that I didn’t know I was taking.

CK: Tell me more.

SH: It’s a hard thing to explain. I was off it for about three months, and I just remember that I started going to the gym again. I had more energy again. Everything felt like it had more possibility and excitement. I started listening to music again. I was traveling and cooking and noticing men. Life felt more textured. Multidimensional, I guess. I’d been on the pill for over a decade, and all that time I never thought twice about taking these hormones … the fact that they were going to influence my brain.

CK: What can research tell us about how birth control influences mood?

SH: Research has shown pretty conclusively that, for some women, the pill can influence mood. And research has also shown conclusively that it can have both positive and negative effects. Some people experience heightened anxiety or depression … but for women who usually get really bad PMS, the pill can be a godsend.

CK: Why does birth control make some people depressed?

SH: The birth control pill lowers levels of this neurosteroid called allopregnanolone, which stimulates GABA [gamma-aminobutyric acid] receptors in our brains. Stimulating these receptors kind of slows our brains down, making us less anxious and more relaxed. The research finds that being on [hormonal birth control] for any period of time substantially decreases levels of allopregnanolone, in the blood and in the brain. This is the leading theory on why birth control sparks anxiety or depression. The brain is just overwhelmed, unable to slow itself down.

CK: But you also said that, for some women, birth control can actually help with mood. Why?

SH: Well in a woman’s natural cycle, estrogen and progesterone change really drastically to prepare the body for the possibility of reproduction. Some women just don’t respond to this very well. They get bad PMS. The pill gives your body the same hormonal message basically every time you take it, preventing your body from freaking out from these drastic changes in hormones.

The sort of crappy thing is that the science isn’t yet in a place where we can make good predictions about which camp you’re going to fall into.

CK: We hear that kind of thing all the time with birth control: We don’t have enough information, the science isn’t good enough. So many women are on the pill. Why don’t we have better science already?

SH: Women and women’s issues have really only started to be noticed by scientists recently. Historically the reason for this is rampant sexism: People just didn’t care about women. But it’s not really that way anymore. Now the problem is that doing this kind of research on women is far more expensive and time-consuming than doing similar research on men.

CK: Why is that?

SH: Because of our cyclically changing hormones. Women have three distinct phases of the menstrual cycle, and during each phase each kind of sex hormone is at a very different level. Sometimes, for example, estrogen is high relative to progesterone, and sometimes it’s the other way around.

So this means that, if scientists want to show a relationship between variables, using women as participants, they have to systematically control for hormonal phase. Which means you have to have three times as many female participants, to account for cycle phase, and you have to keep track of it all. It ends up being really expensive, and takes at least three times as long.

CK: In the book, you write about how hormonal birth control could potentially impact our choice of partner. How does that work?

SH: One study divided up a bunch of [heterosexual] married couples based on whether or not they met when the woman was on or off the birth control pill. The researchers found that women who met their partners when they were on the pill, then went off it, experienced a change in their relationship satisfaction. That change was positive for some, negative for others.

Women with more physically attractive partners (levels of attractiveness were rated by an external group) reported feeling more satisfied with their marriage and more sexually satisfied after going off the pill. Women with less physically attractive partners were less satisfied. This all goes to show that women on the pill tend to de-emphasize the element of sexual attractiveness.

CK: How much stock can we put in this research?

SH: Different researchers find different things, which is just kind of the way things work in science. While I was drafting this book, another study found that there were no differences in relationship satisfaction between women who met their partners while on the pill, versus who met them off the pill. And since that study, another, different study has come out, saying the pill actually does change relationship satisfaction.

CK: There are so many contradictions. What are we supposed to take from all of it?

SH: I think it’s critical that the next stage of this research takes into account the specific type of pill that a woman is on. Because different kinds of birth control have different progestins (a synthetic form of progesterone), and the ratio of progestins relative to estrogen also differs. All that is going to affect women’s behavior in different ways. I think these differences are probably playing a hand in the contradictory results.

CK: We’ve talked a lot about the pill, but what about other kinds of hormonal birth control? Do the hormones in an IUD work the same way?

SH: If you have a hormonal IUD, it all ends up in the same place. Hormones are such an effective means of communication in your body because they travel through your bloodstream. And they travel everywhere …. Hormonal birth control works because it gets a message to your brain. It tells the brain not to release these precursor hormones that cause an egg to mature.

CK: But we know that certain types of birth control can affect people in different ways. There are so many types, with slightly different ratios of hormones. How much of this is just about finding the right kind of hormonal birth control for you?

SH: A lot. But the process requires a lot of patience. It requires women to really trust what their bodies are telling them: wait, and try something, and maybe try something else until they find something that works.

CK: So say you’ve read this book and you’re really concerned about the possible negative effects of birth control. But you also really don’t want to get pregnant. What do you do?

SH: There are lots of options. These are all things to keep your eyes open for: Not every woman is going to react to every pill with any or all of the responses I write about in the book. If you think you are experiencing some of this, you can talk to your doctor about possibly switching to a different type of birth control. For women who don’t want to be on [hormones] at all, there are copper IUDs. And condoms are always another option.

CK: Do you ever worry that putting this information out there might make some women choose to go off birth control?

SH: In some ways, I think, the information in this book might actually bring women back to the birth control pill … women who have walked away from it in part because they don’t understand what it’s doing to their bodies.

It would be really hard for me to learn that someone read this book, became alarmed, went off the pill and then became pregnant when they didn’t want to be. I wrote this book to get women to have conversations with their doctors and their daughters and their friends. I also wrote it to help us push for more science. Better science.

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