What happens to the brain during perimenopause?

First, perimenopause is not simply oestrogen levels going down

We tend to imagine menopause as a fairly straightforward hormonal story. Oestrogen goes down, periods eventually stop, the end.

Perimenopause is much messier than that.

During the years leading up to menopause, the ovaries become less predictable. Ovulation happens less regularly, progesterone production changes and oestradiol levels can fluctuate considerably from one cycle to the next.

So rather than following one smooth hormonal decline, the body can spend years dealing with fluctuations which the brain is experiencing too.

Oestrogen is not simply a reproductive hormone.

We usually hear about oestrogen in the context of periods, fertility and pregnancy. But the brain has been responding to it all along.

Oestrogen receptors are found in several brain regions involved in memory, attention, decision-making and emotion. The hippocampus helps us form and retrieve memories. The prefrontal cortex is involved in concentration, planning and holding information in mind. The amygdala plays an important role in emotion and stress.

All three respond, in different ways, to hormonal signalling. And this makes that moment when a completely ordinary word suddenly disappears from your brain feel a little less random.

Oestrogen also interacts with neurotransmitter systems including serotonin, dopamine and acetylcholine and it can influence communication between neurons, synaptic plasticity, blood flow in the brain and the way brain cells use energy.

I am not implying that every forgotten appointment can be blamed on oestrogen.

The brain is far too complicated for that.

But when hormonal signalling is changing repeatedly, it makes sense that some of the systems involved in memory, attention and mood may have to adjust too.

And that brings us to brain fog.

Brain fog is not a medical diagnosis. It is really a name for an experience that can be surprisingly hard to explain.

You are still yourself. You can still work, read, think and make decisions.

But maybe a name takes longer to come back to you. Maybe concentrating feels like more effort than it used to. Maybe you lose your train of thought halfway through a sentence, or walk into another room and immediately forget why you are there.

These experiences are very common during the menopausal transition. A major neurological review published in 2026 estimated that around two thirds of women experience cognitive concerns during this period.

The strange thing about brain fog

A 2026 study looked at cognitive symptoms and cognitive performance in more than 14,000 women in England.

Women going through perimenopause were more likely than premenopausal women to report brain fog and poor memory.

So far, not particularly surprising.

But when researchers actually tested cognition, overall performance looked remarkably similar. There was very little difference in global cognitive ability between women who were premenopausal, perimenopausal and postmenopausal.

The relationship between how foggy someone felt and how they performed on cognitive tests was also fairly weak.

I am not implying that symptoms are imagined. One way I interpret it is that the tests we use to measure cognition may not fully capture what brain fog feels like in everyday life.

Sitting in front of a computer completing a twenty-minute memory test is very different from trying to remember someone's name after a terrible night's sleep while answering an email, thinking about dinner and wondering why you suddenly feel boiling hot.

A 2026 meta-analysis combining 26 studies and 9,428 participants found poorer cognitive outcomes in perimenopausal women compared with premenopausal women overall, although the results varied depending on how menopause stage and cognition were measured.

So the answer is probably somewhere in the middle.

The brain does not suddenly stop working properly during perimenopause. But saying that nothing changes at all probably misses something too.

Sleep may be doing more than we think

Anyone who has had a terrible night’s sleep knows what it does to the brain the next day.

You lose your train of thought more easily. You reread the same sentence. Finding the right word takes longer. Small tasks feel strangely demanding.

Now add perimenopause.

Sleep can become more fragmented during this stage of life. Some women struggle to fall asleep. Others wake several times during the night. Hot flushes and night sweats can make things even worse.

That makes brain fog difficult to untangle.

Is concentration harder because oestrogen signalling is changing? Because you woke up four times last night? Because you are anxious? Or because all three are happening together?

For some women, I would say, it is a mixture.

Sleep is deeply involved in attention, memory and the way the brain processes information.

So sometimes what feels like a memory problem may actually begin the night before.

Hot flushes are a brain story too

Hot flushes are easy to think of as a body symptom. But the process starts in the brain.

A small region called the hypothalamus helps regulate body temperature. During the menopausal transition, changes in oestrogen signalling affect the neural systems involved in that regulation.

The result is that the body can become much more sensitive to small temperature changes.

Suddenly, what would normally be a minor shift is enough to trigger sweating, flushing and that very familiar feeling of being inexplicably boiling while everyone else in the room seems completely comfortable.

That is interesting on its own. But imagine it happening three times during the night....Now it is no longer just a hot flush. It is three interruptions to your sleep.

And the following morning, the fogginess may have less to do with one specific “memory centre” in the brain and more to do with the fact that your brain simply did not get an uninterrupted night.

Mood can change the way we think too

Perimenopause can also mess with mood a little.

For some women, that looks like irritability. For others, anxiety, low mood or just feeling more emotionally “off” than usual.

And when your head is already full, concentrating gets harder.

You can be in a meeting, listening to someone talk, while half your brain is somewhere else entirely, thinking about what you forgot to do, what you need to do later, or why you suddenly feel anxious for no obvious reason.

So sometimes, when you cannot remember something afterwards, the problem may not be memory itself.

Maybe your attention was just split to begin with and that is part of what makes “brain fog” such a messy term.

So, is the brain actually changing?

It seems so.

Brain imaging studies have found changes in structure, connectivity and the way the brain uses energy across the menopausal transition.

Sounds weird, but change does not automatically mean damage.

The brain changes throughout life. Pregnancy changes it. Learning changes it. Ageing changes it. Perimenopause may simply be another period of adjustment.

And interestingly, some studies suggest that certain brain changes may stabilise after menopause rather than continue getting worse.

And brain fog is not dementia

This is probably the most important distinction.

Forgetting a word, losing your train of thought or feeling less mentally sharp during perimenopause does not mean you are developing dementia.

Researchers are interested in the relationship between reproductive ageing and later brain health, but menopause is only one small piece of a much bigger picture.

What about Hormone Replacement Therapy (HRT)?

The obvious question is: if hormones are changing, can replacing them help?

Sometimes indirectly.

HRT can improve symptoms such as hot flushes and night sweats, and if those are ruining your sleep, you may naturally feel clearer during the day.

But HRT is not currently used simply to improve memory or prevent dementia. The relationship between hormones and the brain is far more complicated than assuming that more oestrogen equals better cognition.

So where does that leave us?

Probably with a brain that is adapting. Hormones shift. Sleep changes. Mood changes. Attention can feel less reliable.

And the brain itself may be adjusting to a completely different hormonal environment.

For some women, that adjustment is barely noticeable while for others, it feels like walking around with twenty browser tabs open and no idea which one is playing the music.