Progesterone in women: what it does and how it changes

Reviewed by Emma Carter, Senior Health & Nutrition Editor

Progesterone is the hormone of the second half of your cycle. The name points to pregnancy, but it does more than that. It balances estrogen, steadies mood and sleep, and drives the monthly rise and fall that brings on your period. There is a mechanism behind the mood and sleep part: progesterone is converted in the brain into compounds that act on the GABA calming system, which is also why it is tied to premenstrual symptoms and why it can ease sleep disturbance and mood instability (Int J Mol Sci, 2021). If conception does not happen, the corpus luteum starts breaking down about 9 to 10 days after ovulation and progesterone falls (Int J Mol Sci, 2021). When it runs low, your cycle and your sleep are often the first things to shift.

What progesterone does

Your ovaries make most of your progesterone after ovulation, from a temporary structure called the corpus luteum. Its main jobs:

• Preparing the uterus, thickening and steadying the lining for a possible pregnancy
• Sustaining early pregnancy until the placenta takes over
• Balancing estrogen, keeping the womb lining from overgrowing
• Calming the brain, which affects mood and sleep
• Nudging up body temperature after ovulation

Across your cycle

Progesterone stays low in the first half of your cycle, rises sharply after ovulation, and peaks about a week before your period. If you do not conceive, the corpus luteum breaks down, progesterone falls, and that drop brings on your period. That small rise in body temperature after ovulation is what temperature-based cycle tracking picks up, and our ovulation calculator estimates when the shift is likely.

That same premenstrual fall is why some women get mood changes, bloating or broken sleep in the days before a period, part of PMS for many and more severe in PMDD. If pregnancy happens, progesterone keeps climbing instead.

Progesterone and estrogen: a balance

Progesterone and estrogen work as a pair. Estrogen builds the womb lining in the first half of the cycle; progesterone matures and steadies it in the second half. When you ovulate normally, the two stay in balance. When ovulation does not happen, estrogen can act without enough progesterone to balance it, which is one reason periods turn irregular or heavy. You may see this loose imbalance called "estrogen dominance" online, but it is a description rather than a formal lab diagnosis, so treat confident claims about it with caution.

Through life stages

Progesterone cycles monthly through your reproductive years, climbs through pregnancy, then turns erratic in perimenopause as ovulation gets less predictable. After menopause, with ovulation stopped, your ovaries make very little. Cycles without ovulation, common in PCOS and perimenopause, produce little progesterone even when estrogen is present, which is a frequent driver of irregular or heavy bleeding at these stages.

Signs of low progesterone, and how it is tested

Low progesterone tends to show around your cycle and fertility: short cycles or spotting before a period, irregular or missing periods, trouble conceiving or early miscarriage, and poor sleep or mood dips in the luteal phase. A random blood test says little on its own. Progesterone is confirmed with a test timed to about seven days before your expected period, which also tells your doctor whether you ovulated. It is read alongside your other hormones rather than in isolation.

Progesterone in HRT and contraception

Progesterone matters in menopause treatment. If you still have your uterus, HRT with estrogen alone can thicken the womb lining and raise the risk of cancer there (Int J Mol Sci, 2025), so progesterone or a synthetic progestogen is added to protect it. If you have had a hysterectomy, you usually take estrogen on its own. Micronised progesterone, a body-identical form taken at night, is often chosen and can help with sleep. Progestogens also feature in contraception, in the progestogen-only pill and the hormonal coil, which is why some women notice cycle and mood changes on them.

When to see a doctor

See your doctor if your cycles are short, irregular or marked by spotting, if you are struggling to conceive, or if premenstrual mood and sleep changes are hard to live with. Progesterone is best tested at the right point in your cycle and interpreted alongside your other hormones, so it is worth doing properly rather than from a one-off result.

Frequently asked questions

What does progesterone do?

Progesterone prepares the lining of the uterus for a fertilised egg and helps maintain a pregnancy. Across the menstrual cycle it rises after ovulation and, if there is no pregnancy, falls again to trigger a period. It also balances estrogen and affects mood, sleep and body temperature.

What are the signs of low progesterone?

Common signs include irregular or short cycles, spotting before a period, difficulty getting or staying pregnant, and mood or sleep changes in the second half of the cycle. Because these overlap with other issues, low progesterone is confirmed with a timed blood test, not symptoms alone.

How is progesterone tested?

With a blood test timed to about seven days before your expected period, in the luteal phase, not a random day. This checks whether you ovulated and made progesterone. In a fertility work-up it is often called a day-21 test, adjusted for your cycle length. A random result outside that window says little.

When is progesterone highest in the cycle?

Progesterone rises after ovulation, in the second half of the cycle known as the luteal phase, and peaks about a week before your period. If pregnancy does not occur, it drops and menstruation begins. If pregnancy happens, it keeps climbing instead.

Why is progesterone used in HRT?

For women who still have a uterus, taking estrogen alone can thicken the womb lining and raise cancer risk. Progesterone, or a progestogen, is added to protect the lining. Women without a uterus usually take estrogen on its own.

References

1. Menopausal hormone therapy: risks, benefits and emerging options, a narrative review · International Journal of Molecular Sciences, 2025
2. Progesterone: natural function, levels and side effects · Cleveland Clinic
3. Key to life: physiological role and clinical implications of progesterone · International Journal of Molecular Sciences, 2021