Brain fog in perimenopause

What brain fog feels like

Brain fog is not a medical diagnosis. It is the name women give to a cluster of small lapses that start to feel out of character. The NHS symptom page for menopause and perimenopause puts it plainly as problems with memory or concentration, and lists it alongside hot flashes, poor sleep and mood changes.

Day to day, it tends to show up as:

• a familiar word or name that will not come, mid-sentence
• walking into a room and forgetting why you went in
• reading the same paragraph or email three times before it sinks in
• losing track in a meeting or a conversation when you are interrupted
• taking longer to learn something new, like a new system at work
• more lists, reminders and notes than you used to need

Most of these are about getting information in and pulling it back out quickly. Long-held knowledge, your judgement and your skills at work usually stay where they were, which is part of why the change is so unsettling: you know you can do this, and today it is harder.

What the research says about memory in perimenopause

The best-known evidence comes from the Study of Women's Health Across the Nation (SWAN), which tested 2,362 women in the US every year for four years as they moved through the menopause transition. It measured three things: processing speed, verbal memory (recalling a short story) and working memory.

Women before perimenopause and after menopause scored a little better each time they repeated the tests, as people usually do with practice. Women in perimenopause did not. On processing speed, the late perimenopausal group stayed flat, and on delayed recall of the story both the early and the late perimenopausal groups stopped improving. The authors describe it as women not being able to learn as well as they had before, which matches what many report feeling.

The more reassuring part came later. After menopause, the women's scores went back to rising with practice, at the same rate as before perimenopause. The authors concluded that the thinking difficulties of the transition "may be time-limited". The effect they measured was small, and it was an average across thousands of women, so it cannot predict how your own memory will hold up. It does mean forgetfulness in perimenopause is a recognised pattern with a likely end, rather than a sign that something is wrong in itself.

Why it can feel worse some weeks

Hormone levels in perimenopause rise and fall unevenly, and the other symptoms they bring can weigh on concentration too. The NHS notes that low mood and memory problems can feel worse when you are very tired, and that sleep problems may be worse with night sweats. A run of broken nights can make a week of thinking feel much foggier than the week before.

Stress, anxiety and low mood work the same way. The NHS page on memory loss names stress, anxiety, depression and insomnia as common, treatable causes of memory problems at any age. In midlife these often arrive together with perimenopause, which makes it hard to tell which one is behind a bad patch. Our guide to PMDD or perimenopause may help if your worst days fall in the week or two before a period.

Other causes worth ruling out

Brain fog in your 40s is often perimenopause, but some of the most common alternatives can be found with a simple blood test and are worth asking about:

• Iron deficiency anaemia. The NHS names heavy periods as a very common cause, and lists tiredness, lack of energy, headaches and breathlessness among the symptoms. If your periods have become heavier, read heavy periods and blood clots in perimenopause and mention both at the same appointment.
• Low vitamin B12 or folate. The NHS symptom list includes problems with memory, understanding and judgement, along with tiredness, pins and needles and a sore or red tongue. It advises getting this diagnosed early, because some of the damage from a deficiency left untreated can be permanent.
• An underactive thyroid. It shares tiredness, low mood and slowed thinking with perimenopause. Our page on perimenopause or thyroid sets out which signs point which way.
• Mood and sleep. Depression, anxiety and insomnia, as above, can each cause memory and concentration problems on their own.
• ADHD. If distraction and forgetfulness go back to your school years, read perimenopause or ADHD, which explains why the two are easy to confuse and why ADHD can feel worse in perimenopause.

The full blood count a GP usually orders for anaemia also looks for B12 and folate deficiency anaemia, so one sample can cover the first two.

When to get your memory checked

The NHS advice on memory is simple: most people forget things now and then, and you should see a GP if memory problems are affecting your day-to-day life. It adds that the cause is often not serious, and that getting checked is still worthwhile because treatment for whatever is behind it tends to work better when started early.

I would book an appointment rather than wait for a routine check-up if:

• you are making mistakes at work, missing appointments or forgetting to collect someone, more than once
• it is getting steadily worse over months, with no better weeks in between
• familiar tasks have become hard, like handling change when shopping or following a recipe you know
• you get confused about the time, the day or where you are
• you have trouble following conversations, or the people close to you have started to notice
• it comes with other new symptoms, such as numbness, pins and needles, breathlessness or marked tiredness

Several items on that list come from the NHS description of early dementia symptoms. That does not mean they point to dementia in your case. The NHS stresses that dementia is not a normal part of ageing and that it is better to talk to a GP sooner if you are worried. A short visit that rules things out is a reasonable price for peace of mind.

Sudden confusion is different. According to the NHS, stroke-like symptoms, such as muscle weakness on one side of the body, need urgent medical attention. If confusion comes on suddenly, or arrives with weakness on one side, call 999 in the UK or 911 in the US.

What to bring to the appointment

Brain fog is easy to dismiss in a ten-minute appointment, partly because it is hard to describe when you are on the spot. A few weeks of notes make the conversation easier. Write down:

• examples of what you forgot or struggled with, and on which days
• how you slept the night before, and whether night sweats woke you
• your period dates and how heavy each one was
• your mood, and any stretch of high stress
• every medicine and supplement you take

The NHS also suggests it can help to bring someone with you who can describe the problems you are having. For over-45s, the NICE menopause guideline says perimenopause is usually recognised from symptoms and cycle changes without hormone tests, so your record does much of the work. Our printable symptom diary and appointment checklist has a row for memory and concentration next to sleep, mood and bleeding.

My take

If you are in your 40s, your periods are changing and your memory lapses come and go with your sleep, I would treat brain fog as one more perimenopause symptom and start keeping notes on it. I'd still ask for a blood count, B12 and thyroid test at your next appointment, especially if your periods have become heavier, because those three are quick to check. The cases I would not wait on are the ones that keep getting worse, cause mistakes at work or at home, or that the people around you have started to comment on.

Related reading

Brain fog is one of many symptoms in the overview of perimenopause symptoms and how to track them. If you are not yet sure perimenopause is what is happening, the perimenopause symptom checklist sorts your answers and says what to do next, and the symptoms topic collects every symptom page on the site.