Perimenopause fatigue and brain fog: what causes it and what helps

Why fatigue and brain fog cluster in this window

Because several things that each cause both arrive at the same time. It is rarely one mechanism, and that is the most useful thing to understand about it, since it means there is rarely one fix.

• Fragmented sleep. The biggest driver for most women. Sleep in the transition is broken more often, and broken sleep produces fatigue and poor concentration on its own in anyone, at any age.
• Night sweats. Waking hot several times a night costs you the deep sleep that daytime function depends on, and you may not remember waking at all.
• Mood and anxiety. Risk of low mood rises through the transition. Slowed thinking, poor concentration and exhaustion are core features of depression and anxiety, not side notes to them.
• Iron status. Perimenopausal bleeding is often heavier and less predictable, and heavy bleeding depletes iron. Low ferritin causes fatigue and poor concentration well before it shows up as anemia on a blood count.
• Thyroid function. An underactive thyroid is more common in women and more common with age, and it produces the same fatigue, fog, weight change and hair thinning.
• The hormonal shift itself. Estradiol fluctuates rather than gliding down, and it acts on brain regions involved in memory and attention as well as on sleep and temperature regulation. Word-finding trouble and forgetfulness are commonly reported through the transition.
• Everything else happening at 45. Career load, teenagers, aging parents, alcohol, and less training than you used to do. These are not a lesser explanation, they are part of the same picture.

Brain fog in this window is a common complaint, and on its own it is not a sign of dementia. It is also not something to self-diagnose. If memory changes are getting steadily worse rather than fluctuating, if other people have noticed them, or if they are affecting your safety at work or driving, that is a reason to be assessed rather than reassured by a web page.

What to check first, before you buy anything

This is the order that matters, and it is the opposite of the order the internet sells you. Sleep, iron and thyroid come first because they are common, they are testable, and treating them changes how you feel in a way nothing on a supplement shelf does.

What actually helps, in order of how well it is supported

Ordered honestly. The things at the top are unglamorous, and they are also the ones with the strongest evidence behind them.

• 1. Treat whatever the work-up finds. Correcting iron deficiency, treating an underactive thyroid, treating obstructive sleep apnea or treating depression will do more for fatigue and fog than anything else on this list. If one of those applies to you, it is not optional and nothing else substitutes for it.
• 2. Fix sleep deliberately. Cognitive behavioral therapy for insomnia, usually shortened to CBT-I, is the recommended first-line treatment for chronic insomnia, ahead of sleeping tablets, and it is available in person and through structured programs. Consistent sleep and wake times, a cool bedroom, and moving alcohol away from bedtime attack the same problem.
• 3. Treat hot flashes and night sweats if they are what wakes you. If your sleep is broken because you are waking hot, that symptom is treatable, and there are both hormonal and non-hormonal prescription options. That is a conversation with your own clinician, and for a lot of women it is the most direct fix available.
• 4. Train, specifically. Regular aerobic exercise and resistance training are consistently linked with better sleep, mood and cognitive function, and resistance work protects the muscle and bone that midlife quietly takes. Start smaller than you think and keep it boring.
• 5. Protect the basics. Enough protein, daylight in the morning, caffeine early rather than late, and alcohol treated as the sleep disruptor it is rather than the wind-down it feels like.
• 6. Reduce the cognitive load you are carrying. Lists, calendars, single-tasking and writing things down are not defeat. They are the practical intervention women actually rate when the fog is at its worst.

On hormone therapy. Menopausal hormone therapy is the best-established treatment for hot flashes and night sweats, and for many women that is what unblocks sleep and everything downstream of it. Expert Health does not offer it, so we have nothing to gain from you choosing it or not choosing it. If you have not had that conversation with your own clinician or a clinician with menopause training, have it, and make the decision with them rather than with a web page.

What is not worth your money

When this needs an appointment rather than a plan

• Fatigue with breathlessness, palpitations, or very heavy periods, which points at iron and needs testing rather than guessing.
• Memory changes that are getting steadily worse, that other people have noticed, or that affect your safety at work or driving.
• Low mood that has lasted weeks, or any thoughts of harming yourself, which is urgent care rather than a hormone question.
• Snoring, gasping or choking in your sleep, or waking unrefreshed no matter how long you were in bed.
• Menopausal symptoms before the age of 40.
• Sudden or severe fatigue with weight loss, fever, or any other new symptom you cannot explain.

If you are not yet sure whether what you are experiencing is the transition at all, start with what the symptoms of perimenopause actually are, which covers the overlap with thyroid disease, anemia, depression and sleep disorders in more detail.

Where a prescribed option might fit

Last on the page, deliberately. If the work-up above has been done, the treatable causes have been treated, sleep is handled or is being handled with a clinician, and you still want to talk about something else, that is a reasonable point to have a conversation. It is not a reasonable place to start.

Expert Health offers NAD+ and sermorelin, and the honest position on both is the same. Neither is FDA-approved for energy, focus or anything to do with the menopause transition. Neither is hormone therapy, neither does what hormone therapy does, and neither is a reason to decline it. The human evidence is thin in both cases: NAD+ precursors reliably raise blood NAD+ levels, and rigorous randomized trials have largely failed to show that raising them changes how people feel, while the sermorelin evidence base in healthy adults is early and built on small studies.

• A free call with a health specialist, with no obligation to buy anything
• An honest answer about the evidence, including when the answer is that this is not the right thing for you
• A US-licensed provider who reviews your history and can decline to prescribe
• If something is appropriate, medication compounded by a licensed US pharmacy, shipped free, with provider check-ins

Expert Health does not provide menopausal hormone therapy and does not diagnose perimenopause. Compounded medications are not FDA-approved, and NAD+ and sermorelin are not FDA-approved for the goals people ask about them for.

Frequently asked questions

Sources

1. Menopause symptoms and relief · Office on Women's Health, US Department of Health and Human Services
2. The menopause years · American College of Obstetricians and Gynecologists
3. Thyroid disease · American College of Obstetricians and Gynecologists
4. Effects of nicotinamide riboside on NAD+ levels, cognition, and symptom recovery in long-COVID: a randomized controlled trial · eClinicalMedicine, via PubMed, 2025