Progesterone in perimenopause: the hormone that goes first

Why it falls first

Progesterone comes almost entirely from the corpus luteum, the structure left behind in the ovary after an egg is released. No ovulation, no corpus luteum, essentially no progesterone.

Anovulatory cycles become progressively more common through perimenopause, and crucially they can still produce a bleed that looks entirely ordinary. So progesterone can be absent for several months of the year while everything appears normal from the outside.

Estrogen meanwhile is still being produced and is swinging, sometimes to levels above the premenopausal range. The early transition is therefore often a relative progesterone problem rather than an estrogen deficiency.

What that explains

• Heavier, longer, more clotted periods: the lining builds without progesterone organising its shedding
• Shorter cycles: the first half of the cycle compresses as follicles are recruited faster
• Worse premenstrual symptoms: the loss of progesterone's calming metabolite in the second half
• Lighter sleep and small-hours waking: progesterone's metabolite allopregnanolone acts on the GABA system, the brain's main inhibitory pathway
• New anxiety with a physical quality: the same GABA route, now intermittent and unpredictable
• Breast tenderness and fluid retention: estrogen acting with less opposition

Progesterone is not the same as progestogen

The terminology causes real confusion and the distinction has clinical weight.

Progesterone means the hormone the body makes. Micronised progesterone is a body-identical form of it, licensed and prescribed. Progestogen, or progestin, is the general term covering synthetic compounds that act on progesterone receptors — a diverse group with different effects.

They are not interchangeable in experience or in evidence. Micronised progesterone is often better tolerated for mood-related side effects, and observational data suggests a more favourable breast and cardiovascular profile than some older synthetic progestogens, which is why it is frequently preferred in current practice.

Why progesterone is included at all

For a woman with a uterus taking estrogen, progestogen is not optional. Estrogen stimulates the womb lining, and without adequate opposition that stimulation can progress to hyperplasia and endometrial cancer.

The route can vary — oral micronised progesterone, or a hormonal intrauterine system delivering it locally, which some women tolerate better because systemic exposure is lower.

After hysterectomy the requirement disappears, and estrogen alone is the standard approach.

Progesterone cream, and why it is a problem

Over-the-counter progesterone creams are widely sold for perimenopausal symptoms. The concern is not the concept but the absorption: they generally do not deliver enough progesterone to protect the womb lining.

Anyone using estrogen alongside a cream rather than an adequate prescribed progestogen may have unprotected endometrium, and cases of hyperplasia associated with this pattern have been reported. It is worth establishing directly rather than assuming.

When to see someone

Heavy bleeding, worsening premenstrual symptoms or new small-hours waking in your forties fit this pattern and are treatable. The hormonal intrauterine system in particular addresses several of them at once and also provides contraception.

If you use estrogen and have a uterus, confirm that your endometrial protection is adequate and prescribed, not a cream.