You are standing in the supermarket and you cannot find the word for bin bags. It is simply not there. And at 44, you are quietly terrified it is the start of dementia.

Dr Mayoni Gooneratne, PHC's Chief Functional Medicine Officer, hears a version of this from women often. If it rings a bell, she wants you to know it is very common. "Brain fog in the perimenopause is real, it's not your imagination," she says, and for the large majority of women it is not early dementia. She says that plainly because, in her words, "fear is a huge part of the suffering that I hear from women a lot of the time."

What perimenopause brain fog feels like

Word-finding is the classic sign. Dr Gooneratne also describes losing your train of thought, forgetting the name of your boss while you are talking to them, and "forgetting that you even forgot." Brain fog is not a recognised medical symptom, which is one reason it is so often missed.

What is happening in your brain

Oestrogen is not just a reproductive hormone. "Your brain is studded with oestrogen receptors," says Dr Gooneratne. Oestrogen influences verbal memory, attention and how quickly you retrieve words, which is exactly why brain fog so often shows up as searching for a word. "The word's there, and then suddenly it's gone."

Through perimenopause, oestrogen fluctuates wildly. A brain that relied on a steady signal now has to work with an unstable one. Dr Gooneratne compares it to a radio that is not quite picking up the station, so you have to strain to hear the message.

Progesterone changes too, and it drops sharply. It has calming, sleep-supporting effects in the brain through its action on GABA receptors. Together, these shifts create the combination so many women describe to her: foggy, revved and exhausted, all at once.

Hormones are not the whole story

Dr Gooneratne also looks at the foundations underneath:

  • The quality of your sleep and how your body clock is working
  • Your gut health, and whether your microbiome is diverse enough to support brain function through compounds such as butyrate
  • Iron, thyroid function and B12
  • Alcohol
  • The sheer cognitive load of being a woman in her forties or fifties, running a household and a job, possibly with teenagers and ageing parents at the same time

For her, brain fog is a convergence. "The hormones might kind of light the match," she says, but sleep deprivation, stress load and low iron are "the fuel".

What a standard appointment can miss

A typical appointment for brain fog may look at your age and send you for a memory test. Dr Gooneratne takes a thorough history and joins the dots with you. That includes:

  • Sleep quality, not just hours. "I want your sleep quality, not just your sleep hours." At PHC this is tracked through PHC Connect, the clinic's health dashboard.
  • Iron stores, thyroid function and B12.
  • Your medications. Some brain fog can be related to medications and past prescriptions.
  • Your cycle. Brain fog often tracks with the menstrual cycle, and if it does, "that really tells you something."

What helps with perimenopause brain fog

Dr Gooneratne is clear that these all work together, so they are in no particular order.

Sleep. "You can't out supplement chronic sleep deprivation."

Hormone support, where it fits. For women whose fog sits alongside hot flushes and cycle changes, body-identical HRT will often improve brain fog along with other symptoms. She does not promise that HRT cures everything, but better sleep supports cognitive function, which is one significant reason to manage symptoms such as hot flushes. HRT is a decision to make with a doctor who knows your full history.

The unglamorous basics. Get your iron and B12 levels checked. Bring your alcohol down. She understands that "the 7 p.m. glass of wine is doing some emotional labour in your life," but it is doing you no favours.

Movement. "Exercise is one of the most reliable cognitive supports that we have at any age."

When brain fog needs a different assessment

Many women tell Dr Gooneratne that their fog fluctuates. It is better on holiday, worse when they are exhausted and definitely worse after a bad night. That pattern is reassuring.

The pattern that needs real assessment is fog that steadily and progressively worsens over months, or that comes with other neurological signs and symptoms. If that is you, do not rely on a blog post. Get assessed properly by a neurologist.

If you are not sure whether perimenopause is part of the picture for you, read the first signs of perimenopause.

Frequently Asked Questions

Is perimenopause brain fog early dementia?

For the large majority of women, no. Fog that fluctuates, better on holiday and worse when you are tired or have slept badly, is a reassuring pattern. Fog that steadily worsens over months, or comes with other neurological symptoms, needs proper assessment by a neurologist.

What does perimenopause brain fog feel like?

The most common sign is searching for words: the word is there, and then it is gone. Women also describe losing their train of thought, forgetting names mid-conversation and forgetting that they forgot something.

Why does perimenopause cause brain fog?

The brain has oestrogen receptors, and oestrogen influences verbal memory, attention and word retrieval. In perimenopause, oestrogen fluctuates wildly and progesterone, which supports calm and sleep, drops. Poor sleep, stress, low iron and other factors often add to it.

Will HRT fix my brain fog?

For women whose brain fog comes alongside hot flushes and cycle changes, body-identical HRT often improves the fog along with other symptoms. It is not a cure for everything, and it is a decision to make with a doctor who knows your history. Sleep, iron, B12, alcohol and movement still matter.

Do brain supplements work for perimenopause brain fog?

Supplements have an important role to play in your health, but they cannot overrule lifestyle challenges. As Dr Gooneratne puts it, "you can't out supplement chronic sleep deprivation." Testing comes first, so you know whether there is a genuine deficiency, such as low iron or B12, to address.

Can low iron or thyroid problems cause brain fog?

Yes, they can contribute. Dr Gooneratne checks iron stores, thyroid function and B12 as part of assessing brain fog, alongside sleep quality, medications and how your symptoms track with your cycle.

Does brain fog get worse at certain points in my cycle?

It can. Brain fog often tracks with the menstrual cycle, and noticing that pattern is a useful clue that hormones are playing a part.