Dr Sylvia Kama-Kieghe, FRCGP — NHS GP & Women’s Health Doctor

You pause mid-sentence because the word you want just isn’t there. You walk into a room and forget why you went in. Then you wonder: “Is this early dementia?”  
Brain fog can happen during perimenopause, and there are reasons why your memory and concentration may feel different.

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How your brain adapts to falling oestrogen 

Oestrogen is not just a reproductive hormone. Your brain cells need it to turn fuel into energy. 

When oestrogen falls through perimenopause:

• The parts of the brain involved in memory and finding words use less energy.
• In some of these areas, blood flow increases.
• This suggests the brain is building new supplies to compensate for the change.

Brain scans of women aged 40 to 65 found these changes in areas involved in memory and perception. 

Two years later, some of the changes had stabilised or even reversed. The women whose brains recovered best also had better memory scores. 

This suggests that brain fog around perimenopause is about brain adaptation rather than progressive deterioration. 

What can contribute to brain fog? 

Two important factors are:

1. Sleep: Night sweats can wake you during the night and make it difficult to get the deep sleep your memory needs. Sleep loss can affect your ability to recall words.

2. Mood: Brain fog can track with perimenopause symptoms, particularly depression and low mood. When your mood is low, attention can split, making it harder to hold information long enough to store it.

Perimenopause can also affect verbal learning and verbal memory. This may mean struggling to remember names, words, or the title of a film or book.

These changes can improve after the transition.  

Four things worth checking  

Some other conditions (which cause ‘brain fog’) can be reversible if they are found early. 

Ask your doctor about:  

• An underactive thyroid
• Vitamin B12 deficiency
• Iron deficiency, especially if you have had heavy periods or changes in bleeding
• Sleep apnoea, particularly if you snore heavily or wake feeling unrefreshed

When should you get help?   

Memory changes deserve proper review if they affect daily life, such as:

• Mixing up medication
• Missing appointments
• Problems with finances
• Getting lost somewhere familiar
• Persistent language difficulties
• Struggling with tasks you have done for years

Also speak to your doctor if there are changes in personality or behaviour, or your memory is steadily getting worse rather than coming and going. 

Key takeaway

Brain fog can be part of perimenopause, and it does not automatically mean dementia. But memory changes that are persistent, steadily worsening, or affecting daily life should be properly checked rather than simply assumed to be perimenopause. 

⚠️ Important Disclaimer — If you are concerned about changes in your memory, focus, and ability to find words during perimenopause, or if anything concerns you, speak to your doctor. This information is for educational purposes only and should not replace an assessment by a healthcare professional. 

More Reading

• Breaking the Silence: Addressing Embarrassing Symptoms of Menopause
• 10 signs you’re already in perimenopause — and you had no idea
• Why Perimenopause Is The MOST Important Time of Your Life
• 8 Supplements for Energy and Focus To Boost Your Brain Power
• 10 Signs You’re Already in Perimenopause — And What to Do Next