Progesterone is present in the body at 100 to 300 times the concentration of estrogen
Estrogen often takes center stage, especially in menopause care. Many women are told they can’t take estrogen without also taking progesterone, not because it’s equally important, but because progesterone helps protect the body from estrogen’s unopposed effects. Progesterone is essentially treated as a buffer.
Estrogen has been widely considered the primary female sex hormone, largely because of its role in stimulating tissue growth. Estrogen drives many of the physical features we associate with femininity, including breast development and the widening of hips during puberty. It’s essential for ovulation, menstruation, and pregnancy, and without it, reproduction would be impossible.
But progesterone may be even more important, and it rarely gets the attention it deserves. Its very name comes from its central role in fertility: “pro-gestation,” the hormone that supports pregnancy. But its influence extends far beyond reproduction. Progesterone is a master regulator. It stabilizes tissues, protects against inflammation, supports metabolic balance, and helps the body respond to stress in healthy ways. Unlike estrogen, which tends to stimulate, progesterone calms, shields, and repairs.
These hormones are commonly misunderstood not just in their function, but also in how we measure them.
On lab tests, estrogen and progesterone are measured in different units because they exist at vastly different concentrations in the body. For example:
Estrogen is typically measured in picograms per milliliter (pg/mL). A picogram is one-trillionth of a gram. It’s measured in such small units because it’s incredibly potent. The body only needs very small amounts of estrogen to have strong biological effects.
In contrast, progesterone is measured in nanograms per milliliter (ng/mL). A nanogram is one-billionth of a gram. This is because it’s produced in much larger quantities. In fact, one nanogram equals 1,000 picograms, so even if the number looks smaller, the actual amount of hormone is significantly greater.
During the luteal phase, a woman’s body typically produces 10 to 30 nanograms of progesterone per milliliter of blood, while estrogen (specifically estradiol) stays around 100 to 300 picograms per milliliter.
Since one nanogram equals 1,000 picograms, that means progesterone levels are roughly 100 to 300 times higher than estrogen.
This is like a teaspoon of estrogen compared to a gallon of progesterone.
Even throughout most of the follicular phase, when progesterone levels are considered “low,” the concentration of progesterone remains elevated above estrogen. It is only in the final day or two before ovulation that estrogen briefly surpasses progesterone in concentration. This short window marks the estrogen surge that triggers the LH spike and leads to ovulation, after which progesterone rises sharply and once again becomes the dominant hormone.
Most people often compare the two hormones by their numbers alone, without considering the units. This leads to a skewed perception—where estrogen appears “higher” or more dominant, simply because its levels are presented in smaller units. In reality, progesterone is often tens or even hundreds of times more concentrated.
Even during the third trimester of pregnancy, both estrogen and progesterone reach the highest concentrations they will ever attain in the human body:
- Estradiol (the main form of estrogen) can rise to around 25,000–40,000 pg/mL.
- But progesterone can reach approximately 200,000 pg/mL.
So, progesterone is still 5-8 times higher than estrogen.
When it comes to HRT, hormone balance, etc., estrogen usually gets most of the attention. But our physiology shows us that progesterone is even more important. We need both hormones, but we need them in the right proportions.
Progesterone stabilizes tissues. It ensures that cells differentiate, and that tissues stay organized, functional, and safe.
Progesterone promotes a healthy cellular metabolism, helps cells use oxygen efficiently, reduces inflammation, balances blood sugar, and protects against overstimulation by estrogen. It calms the nervous system, supports deep sleep, stabilizes mood, and nurtures the uterine lining for pregnancy. It strengthens bones, protects brain tissue, and even supports thyroid function.
Estrogen is a growth promoter—it tells tissues to multiply and expand. But unregulated growth can quickly become dangerous if not balanced. And in general, we need little tissue growth (except during puberty, menstruation, pregnancy, and injury).
Estrogen also stimulates excitatory neurotransmitters, it can raise cortisol, influence blood flow and cardiovascular health, cause weight gain, and increase fluid retention. In high amounts, it can heighten sensitivity to stress, amplify inflammation, and trigger histamine reactions. It affects nearly every system in the body – the brain, the bones, the immune system – sometimes in helpful ways, but often in ways that require careful regulation.
Without enough progesterone to balance it, estrogen’s effects can become excessive, and even dangerous. So, progesterone deserves more than a supporting role.