Perimenopause fatigue: what it feels like and what's causing it

Perimenopausal fatigue isn't ordinary tiredness. Women describe it as being weighted down — the sort of exhaustion a good night's sleep doesn't touch, arriving alongside a sense that your capacity has quietly shrunk.

It's real, and it's common. But the most useful thing to know about it is that it frequently has a cause that is neither mysterious nor purely hormonal — and is treatable.

The short version

• Fatigue in perimenopause often runs through something else rather than directly from falling oestrogen.
• Heavy periods are a major and under-recognised cause, via iron deficiency.
• Around 1 in 3 women in the menopause transition experience abnormal uterine bleeding.
• If your periods have got heavier, a full blood count is the thing to ask for.

The bleeding link most articles skip

Perimenopause changes your periods. For a lot of women that means heavier or longer bleeding — and heavy menstrual bleeding is one of the leading causes of iron deficiency.

Iron deficiency causes fatigue. It also causes breathlessness, palpitations, poor concentration and low mood — all of which overlap almost exactly with the things you'd otherwise put down to menopause. Two conditions, one symptom picture, and only one of them gets talked about.

Research published in Menopause, the journal of The Menopause Society, in March 2025 found that abnormal uterine bleeding during the menopause transition was associated with fatigue, and reported that around one in three perimenopausal women experience it. Women in midlife are two to four times more likely to experience debilitating fatigue.

So the chain runs: hormonal change → heavier periods → iron loss → exhaustion. Every link is real, and the last two are fixable.

The test to ask for

NICE guideline NG88 on heavy menstrual bleeding recommends a full blood count for women being investigated for heavy periods. That's the baseline test, and it's the one to make sure happens.

There's a recent change worth knowing about. NG88 previously advised against routinely testing serum ferritin — the marker for stored iron. NICE removed that recommendation on 7 July 2026.

Be precise about what that means: the guidance no longer advises against ferritin testing. It doesn't mean ferritin is now routinely recommended for everyone. What it means practically is that if you have heavy periods and unexplained fatigue, asking about ferritin is a more reasonable conversation to have than it was a few months ago — particularly if a full blood count comes back normal, since haemoglobin can be normal while iron stores are already low.

This is recent enough that not every article, and possibly not every GP, will have caught up with it.

The other routes

Iron isn't the only path from perimenopause to exhaustion.

Broken sleep. Night sweats wake you. The NHS notes sleep problems are worse when night sweats are present, and that poor sleep leaves you irritable, stressed and anxious. Months of fragmented sleep produces exactly the flattened, unrefreshed tiredness women describe.

Low mood and anxiety. Both are on the NHS symptom list, and both are exhausting in themselves. Fatigue is a core feature of depression, not a side note.

Things that have nothing to do with menopause. Thyroid problems, other causes of anaemia, and a long list of conditions that don't stop existing because you're 47. This is the reason to have fatigue assessed rather than attributed — and the reason I'd be wary of any article that tells you confidently it's your hormones.

What fatigue in perimenopause tends to feel like

Not always the same as ordinary tiredness. Common descriptions:

• Sleep doesn't fix it. You wake unrefreshed regardless of hours.
• It arrives suddenly rather than building through the day.
• Physical heaviness — limbs, not just eyelids.
• It comes with brain fog: the exhaustion and the losing-your-words are one experience, not two.
• It's disproportionate to what you've done.

None of that is diagnostic. But if you've been telling yourself you're just busy, and this list reads as your last six months, it's worth a different conversation.

When to see a GP, and what to say

Book an appointment if fatigue is affecting your daily life — work, driving, looking after people, the things you'd normally manage.

Worth saying explicitly in the appointment:

• How your periods have changed, especially if they're heavier or longer. Don't assume it's a separate issue from the tiredness; it may be the whole explanation.
• Whether you're breathless, dizzy, or getting palpitations. These point towards anaemia rather than away from it.
• What your sleep is actually doing — waking with night sweats is different information from not being able to fall asleep.

And it's reasonable to ask directly: could we check a full blood count?

If it turns out to be iron, that's a genuinely good outcome. Treating iron deficiency addresses both the deficiency and the bleeding causing it — correcting one without the other tends to mean it comes back.

The thing worth resisting

The instinct with fatigue is to absorb it. To assume it's age, or work, or the general condition of being a woman in her forties with too much on.

Some of it may be. But "perimenopause fatigue" is a description, not a diagnosis, and treating it as an explanation is how a treatable iron deficiency goes unfound for two years.

Get the blood test. Then you know what you're dealing with.