Hormonal Changes After 40: What's Actually Happening
← Back to Learn · By Kathryn Carter · Last updated: 16 August 2026
Most explanations of perimenopause start with "oestrogen declines" and stop there. That's true and it's not much use, because the experience doesn't feel like a smooth decline. It feels erratic.
Here's what's actually going on.
It isn't a decline. It's a wobble, then a decline.
You're born with all the eggs you'll ever have. Through your thirties and forties, the number remaining falls, and — more importantly — the ones left respond less predictably to the signals telling them to mature and release.
That's the whole mechanism. Everything else follows from it.
Because ovulation becomes less reliable, the hormones that follow it become less reliable too. Some cycles you ovulate normally. Some you don't. Some produce a surge of oestrogen higher than anything in your thirties.
This is why perimenopause feels chaotic rather than gradual. It is chaotic. Oestrogen can be high one month and low the next, and both feel like something.
Progesterone usually goes first
Progesterone is produced after ovulation. If you don't ovulate in a given cycle, you don't make much.
So in early perimenopause — often late thirties to early forties — progesterone is typically the first to become inconsistent, while oestrogen is still broadly present.
Progesterone has a calming effect on the nervous system and influences sleep. When it drops away, many women notice they feel more wired at night, sleep less soundly, or feel more reactive in the second half of their cycle. Often before any period changes.
If you've felt "different" for a couple of years but your cycle looks normal, this is usually why.
Then oestrogen becomes erratic
Oestrogen doesn't fall in a straight line either. Late perimenopause is often characterised by wide swings — sometimes higher than usual, then dropping sharply.
Oestrogen influences a lot: temperature regulation, serotonin, bone turnover, skin hydration and collagen, where the body stores fat, gut motility, and the tissues of the vagina and urinary tract.
That range explains why the symptom list is so long and so scattered. It isn't that one hormone does one thing badly. It's that a hormone involved in many systems is fluctuating.
The stages, in plain terms
Perimenopause — the transition. Begins when cycles start changing in length or character, ends twelve months after your final period. Typically lasts four to eight years, sometimes longer. Most symptoms happen here.
Menopause — a single point in time, diagnosed retrospectively: twelve consecutive months without a period. The average age in Australia is around 51.
Post-menopause — everything after. Hormone levels are low but stable, and stability is the part that matters. Many women find symptoms settle, while longer-term considerations like bone and cardiovascular health come into sharper focus.
Why blood tests often don't help
A common frustration: you feel unmistakably different, you ask for a test, and the results come back normal.
That's because in perimenopause hormone levels change week to week. A blood test captures one moment. FSH in particular can look entirely normal in a woman who is clearly in perimenopause, then abnormal a fortnight later.
Which is why perimenopause is generally diagnosed on symptoms and cycle changes rather than bloods, particularly over 45. Tests are more useful for ruling other things out — thyroid function and iron studies are usually more informative.
If you're under 45 and your cycle has changed significantly, testing is more relevant, and worth discussing.
What this means practically
Symptoms varying month to month is normal. It isn't you being inconsistent. The underlying hormones are inconsistent.
"Normal" test results don't invalidate what you're experiencing.
Timing matters. Bone loss is fastest in the first few years after your final period, which makes the window either side of it worth acting in. More on bone health after 40.
This is a life stage, not a deficiency state. Menopause isn't a disease. It's a transition every woman goes through, and it ends. Support is worth having; the framing that something has gone wrong with you is not.
Where MyPause fits
MyPause makes products for women through this transition. Hormone Balance Plus (AUST L 470807) is a listed medicine containing vitex, peony, maca, American ginseng, rhodiola, withania, passionflower, lemon balm and magnesium. It helps maintain and support female healthy hormonal balance, helps relieve weariness, tiredness and fatigue in healthy individuals, and contains herbs traditionally used in Western herbal medicine to support a healthy stress response.
If you're not sure where to start, the MyPause quiz walks you through it.
Always read the label and follow the directions for use. If symptoms persist, talk to your health professional. Vitex agnus-castus may affect hormones and medicines such as oral contraceptives. Consult your health professional before use.
Explore Hormone Balance Plus →
Common questions
What age do hormonal changes start?
Perimenopause commonly begins in the early to mid forties, though it can start in the late thirties. The average age of menopause in Australia is around 51.
Which hormone drops first in perimenopause?
Progesterone usually becomes inconsistent first, because it's produced after ovulation and ovulation becomes less reliable. Oestrogen tends to fluctuate widely before falling.
Can I test my hormones to find out if I'm in perimenopause?
Usually not helpfully. Levels vary week to week, so a single test captures one moment. Over 45, diagnosis is generally based on symptoms and cycle changes. Under 45, testing is more relevant — discuss it with your GP.
How long does perimenopause last?
Typically four to eight years, though it varies considerably. It ends twelve months after your final period.
Is perimenopause a hormone imbalance?
No. It's a normal life stage in which hormone production changes as ovulation becomes less regular. It isn't a disorder, and it does end.