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Oral contraceptives have been effectively preventing pregnancy for more than 65 years, but it has only been in the past 10 that scientists – many of them women – have started to seriously examine what effect they have on the brain.

New research is showing that oral hormonal contraceptives may alter the risk of mood disorders such as depression and anxiety, affect the brain’s response to stress and change the structure of certain brain regions. Evidence presented at the European Stroke Organisation Conference on 21 May also shows that women on oral contraception face , when a clot blocks the flow of blood to the brain.

So far, the science still suggests hormonal birth control is largely safe, but it has side-effects that vary with each individual, their age and health history, and the particular formulation of their contraceptive.

“This is a tool to help women control their fertility,” says at the University of California, Santa Barbara. “Now we’re recognising that it was a blunt tool, and we understand there’s more nuance.”

Getting to grips with that nuance will require more investigation, say researchers. However, some of that nascent work is threatened by the chaos surrounding the Trump administration’s efforts to terminate diversity, equity and inclusion policies and to gut federal health funding. So, what do we know now?

Stress and the pill

Birth control came to the US market in 1960, with the UK following in 1961, offering women an unprecedented level of bodily autonomy; and became lawyers, doctors and judges. Now, more than , known colloquially as “the pill”. However, though many studies have demonstrated the pill’s effectiveness at preventing pregnancy, few have investigated the effect exogenous hormones, specifically oestrogen and progesterone, have on the brain. Recent research has – and the results are mixed.

“I don’t think we should all freak out and run to the hills and throw away all of our birth control pills,” says at the University of California, Los Angeles. “But I do think that we should study these things so that we can understand the trade-offs that we’re making.”

Some of those trade-offs may be in mood. have found higher rates of depression in oral contraceptive users, particularly in those just starting to take the pill. Those who display , where abrupt changes in hormones – such as during puberty, pregnancy and the postpartum period – hit particularly hard, may be at a higher risk of negative effects. But the evidence suggests people’s responses are incredibly individual – some on oral contraceptives, and for others, using oral birth control methods for long periods reduces the risk of depression and anxiety.

“What has become increasingly clear is that it all depends,” says at the University of Michigan. Additionally, the different types of oral contraceptives further muddy the waters. The , the combined oral contraceptive pill, contains both oestrogen and one of several kinds of progestin, which are synthetic forms of progesterone. Progestin-only pills, also called “mini-pills”, haven’t been as well studied, and the different kinds of progestin they use each act differently in the body.

One possible explanation for how oral contraceptives disrupt mood is that those on the pill exhibit . This can increase sensitivity to stress and elevate the risk of mood disorders. Other research suggests that sex steroid hormones, such as oestrogen, may modulate the body’s stress response. A 2022 study found that hormonal contraceptive users had both higher levels of cortisol, a steroid hormone, and

Mengelkoch, whose research investigated the mechanisms behind this phenomenon, found at the molecular level than those who don’t. Previous studies have found that oral contraceptive users , says Mengelkoch. Although cortisol is often maligned as the “stress hormone”, that is an over-simplification of a necessary molecule involved in regulating metabolic function and reducing inflammation, as well as helping the body deal with stress. When cortisol doesn’t rise as it should, people still experience stress, but they aren’t as equipped to respond.

“Their bodies aren’t coming online to help them to manage the stressors that they’re experiencing,” says Mengelkoch. “Over time, that might be causing some of the mental health and depression-related outcomes that you see.”

Structural changes

Evidence is also mounting that the use of oral contraceptives changes structures within the brain, with potential for adverse effects. Those at greatest risk of detrimental changes may be teenagers, whose brains are still developing. About use the pill, and they seem to compared with those who never use oral contraceptives or who start later in life. Studies have also shown that women who started using the pill earlier in adolescence had more , an area known for its role in processing fear, than those who started later.

Adult brains also seem to change, although the effect of those changes is unclear. A 2023 study found that adult women using oral contraceptives had a than those who never used or stopped using the pill. Researchers concluded that the changes might imply a structural vulnerability to stress or anxiety disorders, since other studies show a . However, they also caution that more investigation is needed – these studies tend to be small and the association between brain structure and fear .

To try to understand these brain changes – and how best to study them – at the University of Minnesota, Twin Cities, decided to use her own brain as a test subject. Heller, who was 30 at the time of this research, underwent 75 brain scans over the course of a year, covering the time before, during and after using oral contraceptives. She and her colleagues found that the volume of her cerebral cortex decreased by 1 per cent while she was on the pill.

Heller warns that it is too early to say what these changes mean – changes in volume don’t necessarily imply an effect on health or cognition. “Decreases could be a protective factor, could be a risk factor, [or] it could be both,” she says. Furthermore, it isn’t clear what is happening at the microscopic level: “Is it just water that’s changing, or are the actual neural cells changing?”

While any changes may seem alarming, our brains are constantly adapting. “Every time you learn something new, your brain changes. Every time you change your diet, your brain changes,” says Taylor. “That’s why we’re so successful, because our brain can change and adapt to the environments that we’re putting it in.”

Funding cuts threaten research

But though research into the effects of hormonal birth control on the brain have begun to pick up steam in the past decade, changes to the political landscape are threatening to bring this to a halt.

In April, the Trump administration dismissed the team , along with employees at the division dedicated to women’s health and fertility at the Centers for Disease Control and Prevention (CDC). This, say researchers, means the loss of valuable data and guidance on the safety of contraceptives. Meanwhile, women’s health researchers at major universities, including Columbia University in New York, have seen , after the Trump administration forced the termination of grants potentially related to diversity, equity and inclusion. Words triggering immediate scrutiny included “women” and “female”. The funding freeze also prematurely halted investigating the efficacy of and non-hormonal , both plausible alternatives to oral contraceptives.

“It’s unclear how severe the long-term consequences will be, but yes this will hamper research into this question and others adjacent to it,” says Taylor. “No matter where you look, there are going to be fewer trained and motivated people to ask the questions, fewer opportunities to fund the people who are trained and interested, lower likelihood that they’ll have the facilities and resources to conduct the science effectively… When push comes to shove, the research programs that will be considered worthy of funding or safe to pursue are not likely going to be those that focus on women’s health.”

In the meantime, scientists want to stress that research done so far doesn’t point to a need to stop using oral contraceptives. Side-effects are a reality of any pharmaceutical, and, says Mengelkoch: “Oftentimes the benefit of being not pregnant is worth the trade-off of a lot of side-effects.”

Ultimately, birth control is a personal choice, dictated by the circumstances and needs of the individual. “I would never tell anyone who’s having a good experience on their birth control to stop using birth control,” she says. “I wouldn’t even necessarily tell someone who’s having a kind of bad but tolerable experience to change it.”