More than 240 million people across the world use contraceptive medications. In addition to pregnancy prevention, these medications are often prescribed as essential treatments for a range of reproductive and gynecological health needs, including irregular menstrual cycles and pain management; the prevention of pelvic inflammatory disease (PID); management of chronic conditions such as poly-endocrine metabolic ovarian syndrome (PMOS, formerly PCOS) and endometriosis; and as an element of some gender-affirming care. But despite their widespread use, there exists little information about how hormonal contraceptive medications might interact with the body’s response to extreme heat, even as global temperatures continue to rise as a result of climate change.

A new commentary I co-authored on behalf of the Academic Network for Sexual and Reproductive Health and Rights Policy, “Extreme Heat, Hormonal Contraception, and Thermoregulation: A Global Health Perspective,” published this week in The Lancet Obstetrics, Gynaecology, & Women’s Health, highlights this overlooked topic at the intersection of climate change, women’s health, and sexual and reproductive rights.

The reproductive hormones present in hormonal contraceptives can affect baseline body temperature and the mechanisms the body uses to regulate heat, such as sweating and cutaneous vasodilation (or skin flushing). But current research about how these medications might impact heat responses has largely focused on small and short-term laboratory-based studies, most of which examine exercise-related heat exposures in high-income countries. This has left a gap in terms of what the relevant physiological effects of hormonal contraception might mean for people who experience real-world, including longer-term, heat exposure.

This evidence gap is likely of particular concern for hormonal contraceptive users in low- and middle-income countries, where exposure to heat may be greater, and where resources for adaptation, like access to cooling and healthcare, may be more limited. Research on this topic is also lacking among adolescents and girls, transgender populations, and women with chronic conditions.

In addition to the possible clinical outcomes, the above data gaps also call into question whether people can make informed decisions about contraceptive use and exercise their right to health, including sexual and reproductive health, as the world warms. Emerging findings suggest that extreme heat may already be influencing contraceptive use and preference, even causing some women to change their approach to pregnancy prevention. As part of a forthcoming study I’ve been working on with my research team at the University of California, Berkeley, we spoke with one woman in rural Bangladesh who said she switched from the contraceptive pill to condoms due to perceived heat intolerance while on oral contraceptives, and another who said the women in her community “cannot tolerate the [contraceptive] pill … because of the heat.” These findings, along with other emerging research in the field, emphasize the need to better understand contraceptive users’ experiences of heat, in addition to the physiological effects of these medications.

At bottom, the commentary is a call to action for researchers around the world to assess hormonal contraceptives in the context of real-world and chronic heat conditions. Specifically, we urge both policymakers and academics to pay more attention to the experiences of contraceptive users in hot, low- and middle-income countries and to support stronger integration of climate-related risks into sexual and reproductive health research and care. In the commentary, my co-authors and I write that “the physical manifestations of the climate crisis are already shaping key elements of reproductive justice, including women’s rights to choose whether or not to have children, and to raise children in safe and healthy conditions. Extreme heat, for example, is already making pregnancy more dangerous for both mother and fetus. The possibility that rising temperatures may make pregnancy prevention more difficult or more dangerous due to understudied heat-related contraception risks, with harms likely concentrated among already at-risk groups, raises substantial concerns for climate adaptation, gender equity, and sexual and reproductive health and rights.”

As temperatures continue to rise, filing this research gap will be necessary to support the development of equitable climate adaptation strategies. Better evidence will help both health systems and healthcare providers to develop more targeted and appropriate guidance, while working to protect reproductive and bodily autonomy in a changing climate.

Click here to read the full publication in The Lancet Obstetrics, Gynaecology, & Women’s Health and view the complete list of authors.