Many women know the feeling: certain days of the menstrual cycle just come with a lower mood, more irritability, or a shorter emotional fuse. Now, a new study from the University of Barcelona has shown how one of the key hormones in that cycle, progesterone, may actually change the way the brain handles emotional situations.
Published in the journal Psychological Medicine, the research offers a fresh and precise look at how ovarian hormones shape mood in young, healthy women. The findings could pave the way for more personalised ways to assess and treat hormone-related mood disorders, such as premenstrual dysphoric disorder (PMDD), the severe form of premenstrual mood swings.
Why This Matters
Hormones have long been linked to how we feel, but the exact ways in which they do so have been surprisingly hard to pin down. Some women are much more sensitive to progesterone than others, possibly because their brains have more receptors for it. Still, the biological mechanisms behind this link between hormones and emotional ups and downs have remained poorly understood.
The team at the University of Barcelona set out to change that. They looked at how natural levels of two major ovarian hormones (estradiol and progesterone) influence the brain areas involved in managing emotions, and whether this could help explain why mood can shift so noticeably across the cycle.
How the Study Worked
The research involved 116 women with natural menstrual cycles who were not using hormonal contraception. The team used magnetic resonance imaging (MRI) to watch brain activity while the women performed a task designed to test emotional control. Participants viewed happy or angry faces and were asked either to react naturally (approaching the happy face or avoiding the angry one) or to override that instinctive response. The researchers also measured progesterone and estradiol levels using saliva samples, and asked participants about their mood during the previous week.
What the Scans Revealed
When progesterone levels were higher, the brain scans showed something striking: the brain had a harder time clearly distinguishing between emotionally easy and emotionally demanding situations. Specifically, activity patterns in a region called the lateral frontal pole looked more similar to one another, as if the brain was blurring the lines between different emotional challenges.
The women whose brains showed clearer distinctions between easy and difficult emotional situations also tended to report a better mood over the previous week.
Professor Macià Buades, from the UB’s Department of Clinical Psychology and Psychobiology and lead author, said: “The study suggests that if the brain is able to distinguish different emotional situations more clearly, this may help regulate emotions in everyday life.”
He added: “Although we cannot establish cause and effect from a single measure, it is exciting to find information about progesterone that we were previously unaware of.”
What About Estradiol?
The research team expected estradiol, often credited with lifting mood and sometimes used to treat menopausal symptoms, to show a similar but opposite effect to progesterone. It didn’t appear to in this study, but the authors say that may be down to how tricky it is to measure.
Rosamunde Hendricks, co-author of the study and researcher at the Universitat Autònoma de Barcelona (UAB), explained: “We did not observe an effect comparable to that of progesterone for estradiol, but this may be because estradiol is more difficult to measure accurately in saliva. Therefore, we cannot rule out the possibility that estradiol affects the brain. Rather, it may be that the measurement tools used in this study were unable to detect its effects reliably.”
In other words, estradiol might still play an important role; the methods just weren’t sensitive enough to pick it up this time.
A Step Towards Better Understanding
The research offers a crucial piece of the puzzle in understanding how hormones can influence mood, not through vague “chemistry,” but through measurable changes in how the brain processes emotional information. That could matter hugely for women who experience severe mood changes linked to their cycles, as it opens the door to more tailored diagnosis and treatment.
The authors also note that hormonal influences on mood are not a female-only phenomenon, something research has traditionally overlooked. Future studies will need to explore whether similar hormone-emotion links exist in men too.
For now, the message is a reassuring one for women who feel their mood shift with their cycle: the changes are real, they’re biological, and science is beginning to catch up with what many have known all along.
Buades-Rotger, M. et al. (2026). Endogenous progesterone blurs frontostriatal representations of emotion control in healthy young women. Psychological Medicine. DOI: 10.1017/S0033291726105315