You walked into the kitchen with purpose.

Then you stood there. Looking at the kettle. Waiting for your brain to tell you why you came.

Nothing.

Later that day you called your coworker by your sister’s name. You reread the same email three times. You lost a word you’ve used since Grade 3. (It was “colander.” It’s always something like “colander.”)

And somewhere in there, the quiet worry starts: Is this normal? Is this hormones? Is this something worse?

If you’re in your 40s, perimenopause brain fog is a very real possibility. So is the fact that you’re running an entire household on five and a half hours of sleep.

Often, it’s both.

Let’s sort out what’s actually known.

What “brain fog” actually feels like

“Brain fog” isn’t a medical diagnosis. It’s a handy name for a cluster of things that tend to show up together.

The European Menopause and Andropause Society describes it as a mix of cognitive symptoms and fatigue, including:

• Trouble concentrating or focusing
• Forgetfulness and memory slips
• Trouble finding the right word
• Thinking more slowly than usual
• Feeling mentally tired

The NHS lists problems with memory or concentration among menopause symptoms, and notes these can feel worse when you’re not sleeping well and feel very tired.

In other words: the lost keys, the lost word and the lost thread of a conversation all count.

Is brain fog a sign of perimenopause?

It can be. And you’re not imagining it.

Researchers writing in JAMA in 2020 noted that nearly two-thirds of women have subjective cognitive difficulties during the menopause transition, the kind most of us simply call “memory problems.” A 2026 review in The Lancet Obstetrics, Gynaecology, & Women’s Health landed in a similar place: more than two-thirds of women report trouble with memory or concentration during the transition.

So this is common. Very common.

The best-known long-term data comes from SWAN, the Study of Women’s Health Across the Nation, a large U.S. study that has followed women through midlife since the 1990s. In a 2009 analysis of 2,362 women published in Neurology, researchers repeated memory and processing-speed tests over about four years. Normally, people get a little better at tests they repeat. During perimenopause, that expected improvement stalled. After menopause, it came back.

That’s the reassuring part, and it’s worth reading twice: in that study, the dip looked temporary.

A few honest caveats, because The Grounded One insists:

• The changes measured in studies are usually small. Many women who feel foggy still score within the normal range on cognitive tests.
• “For many women” isn’t “for every woman.” A 2022 review for clinicians in Climacteric concluded that memory difficulties resolve for many women but persist for some into postmenopause.
• There’s still a lot researchers don’t know about how brain fog develops and changes over time.

What the evidence does not say: that perimenopause brain fog means you’re heading toward dementia. The same reviews stress that menopause-related brain fog has not been linked to increased dementia risk, and that dementia in midlife is rare.

The other suspects (because it’s rarely just one thing)

Here’s where we get to the stress part of the headline.

Hormones are one possible cause of brain fog. They are not the only one, and they often don’t work alone. The Climacteric review linked cognitive difficulties in midlife not only to changing estrogen levels, but also to hot flashes, sleep and mood.

Before you blame everything on perimenopause, it’s worth looking at the whole line-up.

Sleep. This is the big one. Hot flashes and night sweats can wake you up; so can stress, a snoring partner and a 2 a.m. inbox. Short or broken sleep affects memory and focus for anyone, at any age. Untreated sleep apnea can affect memory too. (Our sleep guide, What Actually Helps With Sleep in Perimenopause?, goes deeper.)

Stress, anxiety and low mood. Mayo Clinic lists stress, anxiety and depression among the treatable causes of forgetfulness, confusion and difficulty concentrating. The NHS also notes that low mood can be part of menopause itself.

Mental load. If your brain is holding the dentist appointments, the permission forms, the dinner plan, your parents’ prescriptions and a work deadline, of course things are falling out. There’s only so much room on the shelf. (We wrote about getting the family calendar out of your head in How Do You Stop Carrying the Entire Family Calendar in Your Head?)

Thyroid. An underactive thyroid (hypothyroidism) can cause tiredness, depression and memory problems, according to Mayo Clinic, and it can also change your periods. Those overlap a lot with perimenopause, which is exactly why it’s worth ruling out.

Iron. Heavy periods are common in perimenopause, and losing blood means losing iron. Iron deficiency anemia can cause extreme tiredness, weakness, headaches and dizziness, which can make thinking feel like wading through mud.

Vitamin B12. Mayo Clinic notes that not having enough B12 can affect memory. A simple blood test can check.

Medications and alcohol. Some medicines, or combinations of medicines, can cause forgetfulness or confusion. Alcohol can also affect sleep and thinking. Worth a look at what’s in your cabinet (and your glass).

Long COVID and other conditions. Brain fog is also linked to long COVID, some chronic illnesses and some treatments. If your fog arrived after an illness, mention that.

Sometimes it is hormones. Sometimes it’s hormones plus no sleep plus a very full life. And sometimes it’s something simple to treat.

This is why “it’s probably just hormones” shouldn’t end the conversation. Sometimes it is hormones. Sometimes it’s hormones plus no sleep plus a very full life. And sometimes it’s something simple to treat.

What tends to help (and how good the evidence is)

There’s no magic pill for brain fog, and you’ll notice we’re not selling one. Here’s what’s sensible, with an honest note on the evidence.

Protect your sleep. Good evidence that poor sleep hurts memory and concentration. If night sweats are waking you, or you might have insomnia or sleep apnea, that’s worth treating in its own right, and your thinking may benefit too.

Move your body. Regular physical activity is one of the general strategies EMAS recommends for brain fog, along with managing stress and taking regular breaks. It also helps sleep and mood. You don’t need a new fitness personality; a walk counts.

Write it down. All of it. This isn’t a cure. It’s relief. Lists, a shared family calendar, phone reminders, a notebook by the bed for the 11 p.m. “don’t forget” thoughts. Every item on paper is one less item your brain has to hold. (If you like a guided page, our own Twice Daily journal gives you five minutes morning and night to empty your head. Think of it as a place to offload, not a fix.)

Lighten the load. Hand off whole jobs, not just tasks. Say no to one thing this week. Single-tasking beats juggling when your focus is thin.

Look after mood and stress. A small 2024 meta-analysis found that CBT-based programs for menopause modestly reduced memory and concentration difficulties. The evidence is limited, but it’s promising, and CBT also has good evidence for mood and sleep problems.

Keep the long game in mind. Things that protect your brain over time are the same boring heroes as always: managing blood pressure and blood sugar, not smoking, keeping alcohol within guidelines, staying social, and getting your hearing checked if it’s slipping.

What about hormone therapy? It’s a fair question, and one for your clinician. Hormone therapy is the most effective treatment for hot flashes and night sweats, so if those are wrecking your sleep, treating them may help how you feel during the day. But the 2022 Climacteric review was clear that hormone therapy is not recommended at any age to treat cognitive concerns at menopause or to prevent cognitive decline or dementia. Bring the whole symptom picture to your appointment, not just the fog.

And supplements? You’ll see plenty of “focus” and “menopause brain” products online. We’re not recommending any of them. Popular isn’t the same as proven.

When to see a doctor

Book an appointment if:

• The fog is getting worse over time, not just coming and going
• It’s affecting your work, safety or independence (missing important deadlines, getting lost in familiar places, leaving the stove on)
• Other people are noticing changes in your memory, mood or behaviour
• You also have signs of something else: very heavy periods, feeling cold all the time, unusual tiredness, low mood that won’t lift
• It started after an illness, a head injury or a new medication

Call 9-1-1 right away for sudden confusion, trouble speaking or understanding speech, face drooping, arm or leg weakness on one side, sudden trouble seeing or a sudden severe headache. These can be signs of a stroke, and stroke is a medical emergency.

If low mood has turned into thoughts of not wanting to be here, please reach out now: call or text 9-8-8 (Canada) or 988 (U.S.), any time.

Questions to bring to your appointment

Then ask:

1. Could this be related to perimenopause?
2. Could sleep, mood or stress be playing a part?
3. Should we check my thyroid, iron or B12?
4. Could any of my medications be contributing?
5. If hot flashes or night sweats are affecting my sleep, what are my treatment options?
6. What changes would mean I should come back sooner?

You’re not being dramatic. You’re being specific. That helps everyone.

The Grounded One’s take

Brain fog in your 40s is real. It’s common. And for many women, it’s not forever.

But it’s also not always “just hormones.” It’s frequently hormones and broken sleep and a brain that’s been holding everyone’s schedule for fifteen years.

So don’t dismiss it as getting older. Don’t panic about it either.

Get curious instead. Track it. Rule out the easy fixes. Take a few things off your plate. And bring specific questions to someone who can help.

If your brain feels full, maybe it’s because it is. That’s not failure. That’s a signal.

ASK MUDDY

What’s the strangest thing you’ve forgotten this month? (Ours: the word “colander.” We’ll be thinking about it for a while.)

JOIN THE MUDDY COMMUNITY

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KEEP READING: THE MUDDY PERIMENOPAUSE GUIDE

Could this be perimenopause? → Perimenopause or Just Life? The Symptoms Women Keep Explaining Away

Not sleeping? → What Actually Helps With Sleep in Perimenopause?

Always tired? → Why You’re Tired Even When You’re Doing Everything “Right”

ABOUT THE MUDDY WELLNESS DESK

The Muddy Wellness Desk explores the health questions women are actually asking, from sleep and hormones to energy, stress, movement and the realities of feeling well in a busy life.

Featuring The Grounded One: calm answers for complicated lives. Research obsessed. Reads the studies so you don’t have to.

Muddy Wellness content is educational and informational and is not a substitute for individualized medical advice, diagnosis or treatment. If you’re worried about changes in your memory or thinking, talk to your doctor or nurse practitioner.

Sources

• The Menopause Transition and Cognition, JAMA
• Brain fog affects two-thirds going through menopause, yet is poorly understood, University College London
• Effects of the menopause transition and hormone use on cognitive performance in midlife women (SWAN, Neurology 2009; summary), HealthDay
• Brain fog in menopause: a health-care professional’s guide for decision-making and counseling on cognition, Climacteric
• Menopause Essentials: Brain fog, European Menopause and Andropause Society
• Menopause: Symptoms, NHS
• Memory loss: When to seek help, Mayo Clinic
• Hypothyroidism (underactive thyroid): Symptoms and causes, Mayo Clinic
• Iron deficiency anemia: Symptoms and causes, Mayo Clinic
• The effectiveness of psychosocial interventions on non-physiological symptoms of menopause: a systematic review and meta-analysis, Journal of Affective Disorders
• Stroke signs and symptoms, U.S. Centers for Disease Control and Prevention
• Signs of stroke, Heart & Stroke
• 9-8-8 Suicide Crisis Helpline, Canada
• 988 Suicide & Crisis Lifeline, United States