Despite more than half a century of use, there's still plenty we don't understand about hormonal contraception.

By Kasandra Brabaw
March 01, 2019

Since the first birth control pill was approved in 1960, tens of millions of people have used oral contraceptives to prevent pregnancy and regulate their periods. Many have been on the pill for decades. And yet, scientists know basically nothing about how birth control affects our brains.

We know plenty about the ways oral contraceptives can affect our physical health. Common side effects include headaches and dizziness, nausea, decreased libido, and breast tenderness. Many of these side effects are temporary and will go away as you continue to take the pill. Hormonal contraceptives can also sometimes (but rarely) cause more serious side effects like blood clots, heart attack, and stroke and are therefore generally not recommended for anyone who has a heart condition.

Even though mood swings are one of the most commonly reported side effects of hormonal birth control, there’s hardly any research into how the pill interacts with our brains. “There’s really very little research I’m aware of on this topic, despite the fact that the pill has been around for more than half a century,” Justin Lehmiller, PhD, a research fellow at the and author of , tells Health. "The studies that do exist tend to have quite small samples and aren’t well suited to determining cause and effect.” There’s so little research that Lehmiller doesn’t feel confident saying anything about birth control and the brain—except that we need more research.

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Ob-gyn , author of , however, feels quite confident that birth control affects our brains. “To think [birth control] won’t affect the brain would actually be ludicrous,” she says. That’s because birth control was designed as an endocrine disruptor. While we often call certain types of birth control—such as the pill, IUDs, vaginal rings, and skin patches—“hormonal” birth control, there aren’t any "real" hormones in them. Instead, there are chemicals meant to mimic the hormones progesterone and estrogen.

These pretend-hormones, as Dr. Gersh calls them, have some similarities with real hormones but can have different effects. And by essentially “replacing” your body’s real progesterone and estrogen with the synthetic versions, the pill may tinker with your brain, she says. “We do know that hormones are hugely important to brain health and brain function," she says.

For starters, estrogen is involved in maintaining your circadian rhythm, or your internal body clock. Research indicates that when that —which can affect the sleep-wake cycle, hormone release, eating habits, digestion, and body temperature, among other 24-hour cycles—we’re at higher risk for psychiatric illnesses like depression and anxiety.

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Birth control may also alter our gut microbiomes, the community of bacteria that live in our stomachs and intestines, Dr. Gersh says, "and we know that the gut microbiome is related to brain function.” If taking birth control changes the population of bacteria in your gut, and the bacteria in your gut affect your brain, then it stands to reason that taking birth control will also alter your brain. Will it change your brain in good ways or bad? That we still don’t know, because there is so little research—especially research with large-enough sample sizes to say anything conclusive.

There are certain things we can guess at, thanks to the past 50 years of people taking birth control. We know that many people on oral contraceptives report anxiety and/or depression as a side effect. Up to 9% of women who take combined hormonal pills report changes in mood, according to Kelley T. Saunders, MD, an ob-gyn with Banner University Medicine Women's Institute.

Some studies that have looked into this phenomenon suggest that , because they have a family history, are most likely to be triggered by birth control. Other studies claim that women who are on the pill are than women who aren’t on the pill. “There’s a lot of conflicting data, and no consistent evidence,” Dr. Saunders says.

Yet she’s seen birth control actually help some patients with mood disorders such as PMS or PMDD (premenstrual dysphoric disorder). Many of us have likely blamed a crabby mood or two on PMS, but PMDD is more severe. It’s a condition that causes extreme irritability, depression, or anxiety in the weeks leading up to menstruation.

Birth control is one of the common treatment options for PMDD, Dr. Saunders says. “The fluctuations of natural hormone levels may be contributing to these mood disorders,” she says. “And we’ve seen women with pre-existing PMS and PMDD do better on continuous-use hormonal contraceptives.” For some, it seems that a steady level of “fake hormones” is better than up-and-down levels of real ones.

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It’s important to remember, though, that all of this is still theory. Does taking birth control change your gut bacteria and therefore your brain? Does it throw off your circadian rhythm and put you at risk for psychiatric disorders? Does it cure pre-menstruating people of their irritability and depression? Maybe. But science hasn’t conclusively told us any of that yet.

And it’s hard to question nearly 60 years of reproductive freedom based only on theory. Hormonal birth control has without a doubt changed lives simply by making it possible to choose when to start a family. “Overall, oral contraceptives have a number of benefits,” says ob-gyn , who’s also board-certified in maternal fetal medicine. Those benefits include pregnancy prevention, of course, but also clearing acne, treating severe cramping and heavy bleeding, decreasing symptoms of endometriosis, preventing ovarian cysts, treating symptoms of PCOS, and decreasing risk of ovarian and endometrial cancer.

So the first step isn’t to drop your birth control. The benefits still seem to outweigh the costs for many. Instead, we need more research about what birth control is really doing to our brains. As Dr. Gersh points out, “If we aren’t aware of what we’re doing, we’ll never get quality alternatives.”

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