A lot of people think PMDD is caused by “too much” or “too little” hormones. You’ve probably heard terms like estrogen dominance or progesterone deficiency thrown around. But the science is clear: PMDD is not caused by abnormal hormone levels. The hormones themselves are normal. What’s different is how the brain responds to the normal rise and fall of those hormones each cycle. Normal Hormones, Abnormal Response. 

Research consistently shows that people with PMDD have normal circulating levels of estrogen and progesterone, and their hormone changes across the menstrual cycle look the same as women without PMDD. That means it’s not about having “too much” or “too little.” Instead, the core issue appears to be that the central nervous system reacts differently to normal hormonal shifts. 

Specifically, brain chemistry and neurotransmitter systems — especially GABA and serotonin — are unusually sensitive to the normal fluctuation of reproductive hormones like progesterone and its metabolite allopregnanolone (ALLO). In people with PMDD, this sensitivity can trigger intense emotional and physical symptoms during the luteal phase. 

What That Sensitivity Means in Practice

Instead of a hormone imbalance, think of PMDD as a communication problem between your hormones and your brain. The rising and falling of estrogen and progesterone during the second half of the cycle are normal. They’re triggers. The difference in PMDD is that the brain’s response to those normal changes is exaggerated or dysregulated. We are sensitive, and our brain reacts badly to these normal fluctuations. 

This explains why:

• People with PMDD do not have abnormal hormone levels.

• Symptoms consistently appear in the luteal phase and go away shortly after menstruation starts.

• SSRIs can work quickly for PMDD because they help stabilise brain neurotransmitter response rather than “fix” hormones (this is why we can stop and start taking them, unlike treatment for anxiety + depression).

It’s Not Just Hormones, Genetics and Brain Function Matter Too

Other factors likely play a role, including genetics, stress history, and even differences in brain structure and function. That’s why PMDD doesn’t look the same for everyone, and why some people still struggle even when hormone levels are normal. 

What This Means for You

If someone has told you that your hormone levels are out of balance, that your symptoms are “all in your head,” or that you just need to fix hormones to feel better, that’s not what the science shows. Your hormones are doing what they’re supposed to do. The issue is your brain’s response to them.

Understanding that changes how we talk about treatment and self-management. It helps shift focus toward evidence-based approaches that work with neurologic and neurotransmitter pathways, not against them.

Raffi ER & Freeman MP. The Etiology of Premenstrual Dysphoric Disorder: 5 Interwoven Pieces. MGH Center for Women’s Mental Health; published September 2017. (womensmentalhealth.org)