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You’ve been on the pill since high school. It’s served its purpose of preventing pregnancy, but do you really know what it’s done beyond that? You might want to pick up a copy of This Is Your Brain on Birth Control, a book by Sarah E. Hill, PhD. Dr. Hill is a researcher in evolutionary biology as well as a professor at Texas Christian University.

According to Dr. Hill, although women go on the pill for a few reasons (chief among them pregnancy prevention and clearer skin), sex hormones don’t work in such isolated ways. Translation: Sex hormones impact the activities of billions of cells in the body at once, many of which are in the brain. That means playing around with your sex hormones via the birth control pill can influence attraction, sexual motivation, stress, hunger, eating patterns, emotion regulation, friendships, aggression, mood, learning and more. This Is Your Brain on Birth Control seeks to make women aware of everything the pill is doing beyond preventing pregnancy and improving skin.

A few things to note: First, Dr. Hill makes it very clear that she’s completely pro-birth control, and even attributes getting her PhD—and having children when she was ready—to being on the pill. She doesn’t suggest that women stop taking the pill, nor does she refute the revolutionary effect the pill continues to have on women’s personal and professional lives. Second, Dr. Hill recognizes that while her book (and much of the research on birth control) is focused on heterosexual cisgender women, she’s not discounting the experience of other female-identifying folks who aren’t on the pill. Read on for five surprising facts about birth control pills.

RELATED: Which Birth Control Is Right for Me? Every Single Method, Explained

woman holding birth control pills
PhotoAlto/Antoine Arraou/getty images

5 Surprising Facts about Birth Control Pills

1. The Pill Can Change Whom You’re Attracted to (and How You’re Attracted to Them)

One of the most fascinating points in Dr. Hill’s book is that the pill can impact the type of partner you’re attracted to. “Scientists have only recently started to explore this possibility. And although this research is new and the results are mixed, the picture that is beginning to emerge is fascinating. They suggest that the birth control pill might influence everything ranging from whom you pick as your partner to the likelihood that you’ll get divorced.” This can manifest in a number of ways, but it may mean that if you’ve been on the pill for a long time, find a partner, date that partner for a long time and then go off of the pill, you might see them in a different light once your hormones are responsible for regulating themselves.

2. Being on the Pill Can Make You Less Likely to Choose a Partner Based on Aesthetics

Because women on the pill don’t ovulate, they don’t experience the pre-ovulatory estrogen surge that increases attention to markers of genetic quality in men. What does that mean, exactly? While women who aren’t on the pill experience a spike in their attraction to men with strong jaws, deep voices and other traditional testosterone markers while their estrogen levels are high (typically mid-cycle), women who are on the pill will probably place less emphasis on sex appeal when choosing a partner.

3.You're Not *Done* with Birth Control Once You Enter Your 40s

It's obviously harder to get pregnant as you get older, but it's certainly possible. As Colleen McNicholas, DO, assistant professor of obstetrics and gynecology at the Washington University School of Medicine in St. Louis, tells Health, "I can’t tell you the number of times I’ve had a 40-something patient stare at me in shock when I’ve told her she’s pregnant." She told the site that she recommends that women over 40 either take oral contraceptives, which can help relieve the symptoms of perimenopause, or use a hormonal IUD.

4. The Pill Can Make You (Way) Less Interested in Sex

Considerable research finds that women on the pill have lower sexual desire than what is observed in naturally cycling women. Why? The pill suppresses the hormonal cascade that sets in motion the release of a mature egg. Along with that hormonal cascade comes a surge of estrogen that’s known to fuel women’s desire for sex. The pill can also cause women’s levels of testosterone to steeply decline. (Testosterone plays a role in sexual arousal and responsiveness.) Since a lack of sex drive can be a major source of stress in a woman’s life and relationship, Dr. Hill suggests being gentle with yourself if you find yourself in this situation. “Be patient with yourself and your partner as you work together to troubleshoot your birth control options,” she writes. The solution might be as simple as finding a new doctor, a new pill or a different form of birth control.

5. Birth Control Shouldn't Cause Weight Gain

This is one of those really pervasive myths that makes the idea of going on birth control kind of scary for some women. Luckily, it's just that—a myth. Multiple studies have shown either that birth control doesn't cause weight gain, or if it does, it's a very small amount of weight gain. A 2014 study by researchers at Columbia University looked at participants at a moderate weight and those with obesity and found no significant change in body weight or composition after using oral contraceptives. Additionally, a 2016 Cochrane review of 22 previous studies found little or no evidence of weight gain.

RELATED: We Ask a Derm: How Do I Go Off Birth Control Without Breaking Out?

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