"We're concerned about what these effects might mean for contraceptive users exposed to ambient heat for many hours at a time, day after day, with little ability to adapt or recover … which is an unfortunate reality for many women living and working in [LMICs]," researcher Cara Schulte told CG.
The questions have popped up on social media in recent years:
"Can birth control make you overheat easily?" one Reddit user posed in 2022, describing discomfort as temperatures hit 90 degrees Fahrenheit.
"Has anyone else developed issues with severe heat intolerance after getting the Mirena [IUD]?" another asked in 2024, sharing that they could "hardly leave the house if it's above 75 degrees."
Just a few months ago, a runner wondered if taking Yaz [oral contraceptive pills] altered their performance racing in Florida's summer heat: "Within two miles, I knew something was off and I had trouble all day taking in nutrition."
There's good reason to guard against reading too much into social media speculation about contraception and its potential impacts — digital misinformation about reproductive health care has been found to be widespread. But listening to the personal questions and concerns of birth control users is something many contraceptive scientists take seriously in improving their products and patients' comfort.
This week, nearly three dozen health and climate researchers and advocates put their names to new commentary in The Lancet calling for more investigation into whether the use of hormonal contraceptives could exacerbate heat sensitivity and stress. It could be a topic of increasing interest for birth control users around the world as global temperatures rise and exposure to extreme heat expands.
"There is still so much we don’t know," commentary co-author Cara Schulte — a researcher at Climate Rights International and a postdoctoral research associate at the University of California, Berkeley — told CG via email.
Schulte said that we have "a solid body of evidence linking extreme heat exposure during pregnancy to adverse birth outcomes, including stillbirth and preterm birth" but "comparatively less data on how heat affects the pregnant woman herself."
While "available evidence also points to strong associations with adverse maternal health outcomes," Schulte noted that "only a small body of qualitative heat research … actually engages with the perspectives and experiences of pregnant women."
Insufficient attention to the hot-weather experiences of those who can become pregnant appears to have extended to a lack of investigation into the experiences of those using contraceptives amid extreme temperatures. Schulte and her colleagues want that to change.
"My co-authors and I pulled together this commentary article because we see clear gaps in our understanding of how extreme heat intersects with sexual and reproductive health beyond pregnancy," she said. "Hormonal contraception is one of those overlooked areas, and given how widely hormonal contraceptives are used, we felt that it would be important to bring attention to this intersection."
Past and ongoing research indicates that the hormones that are a part of many contraceptives — such as pills, injectables, patches, implants, and intrauterine devices — may affect thermoregulation. That's the biological process that enables a body to maintain an internal core temperature.
"But we don’t know how these associations play out in the real world," Schulte said, pointing to potential discrepancies between laboratory-based studies and impacts in the field.
"We're concerned about what these effects might mean for contraceptive users exposed to ambient heat for many hours at a time, day after day, with little ability to adapt or recover … which is an unfortunate reality for many women living and working in low- and middle-income countries," she said.
Recent studies published in Frontiers Global Health and by the Max Planck Institute suggest shifting weather patterns — from drought to heavy rains — are impacting contraceptive use in low- and middle-income countries (or LMICs) in numerous ways, including through disaster-disrupted access, related income shocks, changes in women's ability to make decisions autonomously, and more.
Schulte's forthcoming research in Bangladesh, cited in the Lancet commentary, indicates that heat sensitivity may also be shaping the choices people make about using contraception.
One person she heard from "reported feeling 'agitated in the heat' when taking the contraceptive pill and therefore switched to condoms," the article noted.
Schulte also told CG that her team "spoke to women who felt that oral contraceptives made them or other women in their community less heat tolerant." Some said this caused them to change birth control methods or interrupt their use.
"When you think about the population-level health effects of skipping birth control doses on hot days, or changing birth control methods in the heat, the potential implications are huge," Schulte said.
And they could be huge for people beyond those who use the hormonal products to prevent pregnancy too.
Many also use hormonal contraception to address a range of serious health concerns, such as heavy or irregular menstrual bleeding. And what about those who use hormonal medications as a part of their menopause care or gender-affirming care?
"The foundation of our concerns here is the association between exogenous hormones and thermoregulatory changes," Schulte told CG. "The missing piece is how those associations translate in the context of specific medications being used in real-world settings. That question applies to other hormonal medications, in addition to contraceptives. So while I can’t speak to the specific evidence on those products, I think it would be fair to ask similar questions about them."
Others are asking these questions.
Research published in 2024, for example, evaluated thermal comfort and thermoregulation among transgender women in Brazil and found that gender-affirming hormone therapy was "linked to heightened heat perception."
Recent reporting from Dialogue Earth on the impacts of extreme heat on the Hijra community of transgender, intersex, and third-gender individuals in India also featured an account wherein an interviewee said that taking her gender-affirming hormone medication increased her sensitivity to the heat.
Schulte said that the co-authors of the commentary on contraception hope it can "draw attention to an understudied issue and encourage further research … including by pushing forward the conversation about what reproductive health and autonomy will look like in a warming world."
Helping to kick start that push, the commentary offers several recommendations.
The co-authors say future research should examine real-world cases of chronic heat exposure across various age groups and populations, including in LMICs, prioritizing user-centered and participatory research that emphasizes lived experiences in all their complexity.
Studies should also "examine how direct and indirect heat and climate effects interact with contraceptive care-seeking behavior and the availability and accessibility of contraceptive commodities and services," according to the co-authors.
In addition to broader supply chain monitoring and bringing together the studies of climate and sexual and reproductive health, the co-authors underscore that individuals need to have access to safe, affordable, and voluntary contraceptive options as well as quality information about those options to protect their well-being and their rights.
Taking this research forward has the potential to fill critical evidence gaps. It could also help health systems develop hot-weather guidance for hormonal contraceptive users, not unlike the guidance more commonly provided to users of mental health, ADHD, and blood pressure medications.
Plus, in addition to improving the user experience for those who rely on hormonal medications, this research could end up helping scientists improve the products themselves.
Some are already looking at how to "heat-proof" contraceptives and other medications so that they don't break down and stop working effectively when they're shipped and stored as temperatures rise.
For Schulte and others, it's time to help ensure that contraceptive users don't break down and wither amid extreme heat either.
Kirsten Krueger contributed to the editing of this article.
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