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Progesterone: definition and meaning

2 min read · Updated October 27, 2026

Definition

Progesterone is a steroid hormone made mainly by the corpus luteum after ovulation, and later by the placenta in pregnancy. It thickens and stabilizes the uterine lining so a fertilized egg can implant, and keeps it in place during early pregnancy. When progesterone falls at the end of the luteal phase, a period begins.

Progesterone across the cycle

PeriodLow. The fall in progesterone is what starts your period.
FollicularStays low while estrogen rises.
OvulationStarts to rise as the follicle turns into the corpus luteum.
LutealPeaks about 7 days after ovulation, then falls if there's no pregnancy.

What progesterone does

  • Builds a soft, nourishing endometrial lining
  • Raises your resting temperature by about 0.3 to 0.5 °C (0.5 to 1 °F) after ovulation, the basis of basal body temperature tracking
  • Thickens cervical mucus, making it less sperm-friendly
  • Can make you sleepier, hungrier and more bloated
  • Breaks down into allopregnanolone, which acts on calming GABA receptors in the brain

Progesterone and mood

Progesterone and its by-products can feel calming for some people and unsettling for others. In PMS and PMDD, the brain seems unusually sensitive to rising and falling progesterone, not to abnormal levels. Synthetic versions in contraception are called progestins.

A blood test about 7 days before your expected period ("day 21" in a 28-day cycle) is used to confirm ovulation. Read more about hormones in the menstrual cycle.

Frequently asked questions

What are symptoms of low progesterone?

Possible signs include a short luteal phase, spotting before your period, and irregular cycles. Only a blood test confirms it.

Does progesterone cause PMS?

Not on its own. Levels are usually normal in PMS; the brain's sensitivity to the rise and fall seems to be the issue.

Why does progesterone make me tired?

Its by-product allopregnanolone has a calming, sedating effect, and the slight rise in body temperature can disturb sleep.

Sources

  1. Cleveland Clinic: Progesterone
  2. MedlinePlus: Progesterone Test
  3. Office on Women's Health: Your menstrual cycle

This page is for information only and isn’t medical advice. If something worries you, please talk to a doctor.

Keep reading

Menstrual cycle hormones: a simple chart of what rises and fallsMenstrual cycle hormones explained simply: how estrogen, progesterone, LH and FSH rise and fall through each phase, and how they shape mood and energy.Luteal phase: definition and meaningThe luteal phase is the part of your cycle from ovulation to your next period, usually 12 to 14 days. Hormones, mood, PMS and why it matters.Corpus luteum: definition and meaningThe corpus luteum is the temporary gland left after ovulation that makes progesterone. What it does, how long it lasts, and how it shapes your luteal phase.Progestin: definition and meaningA progestin is a synthetic hormone that acts like progesterone, used in birth control and hormone therapy. Types, how they work, and effects on mood.Luteal phase: why feelings get louderWhat the luteal phase is, how long it lasts, why progesterone rises and falls, and the common symptoms: PMS, cravings, low energy and mood changes.