Last updated: October 2026
Brain fog is a common way of describing feeling mentally slow, forgetful, unfocused or “cloudy”. It’s a description, not a diagnosis. Common causes include poor sleep, stress, menopause, long COVID, low iron or vitamin B12, thyroid problems, some medicines and low mood. Better sleep, movement and regular meals help most people. See a GP if it lasts weeks.
Below: the signs of brain fog, what causes it and what to try for each cause, how long it lasts and how it differs from ADHD and dementia, how to fix brain fog step by step, how to deal with a foggy day, remedies and supplements (and when they’re worth it), and when to see your GP.
Brain fog symptoms: the signs to look for
- trouble concentrating or following conversations
- forgetting words, names or why you walked into a room
- feeling slow, muddled or “not quite here”
- struggling to make decisions or start tasks
- mental tiredness, often with physical fatigue
A 2025 review of brain fog in long COVID and after chemotherapy found it was consistently linked with cognitive complaints, fatigue and mood changes, and that there’s still no agreed definition.
Signs that point to something worth checking: brain fog that has lasted more than a few weeks, is getting worse, or comes with tiredness, weight change, low mood, feeling unusually cold or hot, or heavy periods. See when to see your GP.
The FSA’s 10mg a day figure is precautionary advice rather than a legal limit, set while longer-term safety research continues. At Evopure we think it is a very cautious figure, and many adults use more. If you go above it, increase slowly, and check with your GP or pharmacist first if you take any medication.
What causes brain fog?
Most brain fog comes from everyday reasons such as short sleep, stress and skipped meals. Some medical causes are easy to test for, though. The NHS lists problems with memory and concentration as a symptom of long COVID, difficulty concentrating or thinking clearly as a symptom of an underactive thyroid, and problems with memory, understanding and judgement as symptoms of vitamin B12 or folate deficiency anaemia. Use the table to match the clues to what to try.
| Cause | Clues | What to try |
|---|---|---|
| Poor or short sleep | Worse after bad nights | A regular schedule. A meta-analysis found sleep loss hits attention hardest. See sleep hygiene, or waking in the night if you wake at 3am |
| Stress and burnout | Overloaded, wired but tired | See burnout symptoms |
| Menopause and perimenopause | Mid-life, with hot flushes or irregular periods | Check the other perimenopause symptoms; see below |
| Long COVID | After a COVID infection, with fatigue | The NHS lists brain fog as a common long COVID symptom; see your GP |
| Low mood or anxiety | Flat, worried, unmotivated | Talk to your GP; see anxiety at night |
| Iron, B12 or folate deficiency | Tired, pale, breathless; heavy periods; vegan diet | A GP blood test. See iron deficiency symptoms, B vitamins and why am I always tired? |
| Underactive thyroid | Tired, weight gain, feeling cold, low mood | A GP blood test. See underactive thyroid symptoms |
| Overactive thyroid | Anxious or irritable, poor sleep, fast heartbeat, weight loss | A GP blood test. See overactive thyroid symptoms |
| Dehydration, skipped meals | Worse late morning or afternoon | Regular water and meals. See the afternoon slump |
| Alcohol | Worse the day after drinking | See hangxiety |
| Some medicines | Started after a new medicine | Ask your pharmacist; don’t stop without advice |
Menopause and brain fog
The NHS lists poor memory, problems concentrating and brain fog as common menopause symptoms, and notes they can feel worse when sleep is disrupted. For most women it improves after the menopause transition. HRT can help with symptoms, and protecting sleep makes a big difference. See perimenopause and sleep and magnesium for menopause. For the full picture, including brain fog vs dementia and which supplements have any evidence, see our guide to menopause brain fog.
How long does brain fog last, and could it be something else?
Brain fog usually lasts as long as whatever is behind it, and lifts once that changes. Here’s what to expect for the common causes, and how brain fog differs from ADHD and dementia, two things people often worry about.
How long does brain fog last?
| Cause | How long it tends to last |
|---|---|
| A few bad nights | Usually days. After a longer run of short sleep it can take more than a few good nights: in one sleep-lab study, people who spent a week in bed for 5 or 7 hours a night were still slower after three nights of 8 hours. See sleep deprivation |
| An illness, including COVID | Weeks, sometimes months. The NHS calls it long COVID when symptoms last longer than 12 weeks, lists brain fog as one of the most common symptoms, and says recovery time is different for everybody |
| Menopause | Months to years, and for most women it eases after the menopause transition. See menopause brain fog |
| Low iron, B12 or folate | Give it weeks rather than days once treatment starts. Iron tablets are usually taken for about 6 months, with repeat blood tests to check your levels are recovering. See vitamin B12 deficiency symptoms |
| Stress, low mood or alcohol | Usually improves as the cause eases |
Brain fog that has lasted for months or years, or keeps coming back without a clear reason, is worth taking to your GP rather than living with.
Brain fog vs ADHD
They can feel alike: losing your train of thought, getting distracted, forgetting things. The difference is timing. ADHD is a lifelong pattern, and the NHS says symptoms usually start before the age of 12, even when ADHD is diagnosed in adulthood. Brain fog is usually a change from how you normally are, often with a cause you can point to, such as poor sleep, illness or menopause.
If you’ve struggled with focus, organisation or restlessness for as long as you can remember, and it affects work, study or relationships, talk to your GP. NICE guidance (NG87) says ADHD should only be diagnosed by a specialist, such as a psychiatrist, after a full assessment, so an online quiz can’t tell you either way. Poor sleep makes both harder; see ADHD and sleep, and for practical tips that help either way, how to focus better.
Brain fog vs dementia
Forgetting words, names or why you walked into a room is very common. The NHS says most people forget things from time to time, and that memory problems can be caused by something common and treatable, such as stress, anxiety, depression or sleeping problems. Only occasionally is memory loss a sign of something more serious, such as dementia.
Dementia looks different. It is not a natural part of ageing, it involves an ongoing decline in how the brain works, and its symptoms usually get worse over time. The NHS lists early signs including memory loss, being confused about time and place, struggling to follow a conversation or find the right word, finding familiar daily tasks hard, and mood changes. Brain fog, by contrast, tends to come and go with sleep, stress and other causes.
See a GP if memory problems are affecting your day-to-day life, are getting worse, or someone close to you is worried. The NHS says it’s important to talk to a GP sooner rather than later if you’re concerned. A GP can also check for treatable causes such as thyroid problems, low B12 or folate, low mood or a medicine side effect.
How to fix brain fog
There’s no instant cure, but most brain fog lifts once you deal with what’s behind it. Work through these steps in order, and give changes a few weeks.
- Look for the cause: use the table above. If it has lasted weeks or comes with other symptoms, ask your GP about a blood test (full blood count, ferritin, B12, folate and thyroid).
- Protect your sleep: the same wake time daily and 7 to 9 hours.
- Move: a meta-analysis found breaking up long sitting with activity gave small improvements in working memory and thinking.
- Eat regularly with protein, wholegrains, fruit and vegetables.
- Drink water through the day.
- Cut back on alcohol and keep caffeine to the morning.
- Do one thing at a time and write things down.
- Manage stress with breaks and slow breathing. See nervous system regulation, and burnout if work has been relentless.
- Get outside in daylight every day.
- Review your medicines with a pharmacist if the fog started after a new one. Don’t stop anything without advice.
How to deal with brain fog on a bad day
On a foggy day, especially at work, aim to get through it rather than fight it: do the hardest task when you’re sharpest, and keep the rest simple.
- a 10-minute walk outside
- a glass of water and a protein snack
- a 10 to 20 minute nap before 3pm. See power nap
- one coffee or tea, ideally earlier in the day
- a written list of the next 3 tasks
- closing extra tabs and putting your phone away. See how to focus better
Brain fog remedies and supplements
The remedies that work for most people are the unglamorous ones in the steps above: sleep, movement, regular meals and less alcohol. No supplement clears brain fog for everyone. Supplements help most when they fix a deficiency, such as iron or vitamin B12, confirmed by a blood test.
- Iron: only if a test shows you’re low. Iron contributes to normal cognitive function and to the reduction of tiredness and fatigue. Too much iron is harmful, so test first. See iron deficiency symptoms.
- Vitamin B12 and folate: the NHS says deficiency is more common in older people, and can happen with a vegan diet without fortified foods or a B12 supplement, or with some medicines such as proton pump inhibitors (PPIs). Vitamin B12 contributes to normal psychological function and to the reduction of tiredness and fatigue. See B vitamins.
- Magnesium: magnesium contributes to normal psychological function and to the reduction of tiredness and fatigue.
- Menopause: for the “best supplements for menopause brain fog” question, see menopause brain fog, where we go through what the evidence does and doesn’t show.
Evopure’s products don’t contain iron or vitamin B12, so they can’t correct a deficiency. Caffeine with L-theanine has some evidence for short-term attention. Claims for “brain fog supplements” often go well beyond the research. See magnesium for focus and brain fog and best supplements for energy.
When to see your GP
See your GP if brain fog lasts more than a few weeks, is getting worse, or affects work or daily life, or if you also have tiredness, weight change, low mood or other new symptoms. Get urgent help if confusion comes on suddenly, or with slurred speech, weakness on one side or a severe headache.
Related guides
- How to get motivated.
- Short on sleep? See sleep deprivation.
- Underactive thyroid symptoms.
- Magnesium threonate vs glycinate vs citrate if you are weighing magnesium for focus.
- For what to put on your plate, see our evidence-ranked guide to brain foods for memory and focus.
- For the menopause-specific guide, including brain fog vs dementia and HRT, see menopause brain fog.
- Decision fatigue: signs and what helps.
- Brain fog in ME/CFS.
- Thinking of trying CBD to clear your head? Read does CBD help focus? first.
- What the research on magnesium L-threonate actually shows.
- Signs of perimenopause, from brain fog to palpitations.
- Brain fog is common with long-term pain too; see fibro fog and other fibromyalgia symptoms.
- For which supplements have real evidence for concentration and which are mostly hype, see supplements for focus and concentration.
- If you’re wondering about CBD and ADHD, our guide covers what the research shows so far.
- Sleep and dementia: when to see a GP.
- Some people try lion’s mane for focus; our lion’s mane guide covers what the small human studies found and whether it is safe.
FAQs
What is brain fog?
A common term for feeling mentally slow, forgetful or unfocused. It’s a symptom rather than a diagnosis.
What causes brain fog?
Common causes include poor sleep, stress, menopause, long COVID, low mood, deficiencies such as iron or B12, dehydration, alcohol and some medicines.
How do I get rid of brain fog fast?
A walk in daylight, water, a protein snack, a short nap or a coffee can help on the day. Better sleep is the long-term fix.
Is brain fog a sign of menopause?
It can be. The NHS lists memory problems, poor concentration and brain fog as common menopause symptoms.
What vitamin deficiency causes brain fog?
Low vitamin B12, folate or iron can contribute. A GP blood test can check.
What are the signs of brain fog?
Trouble concentrating, forgetting words or names, feeling slow or muddled, struggling to make decisions and mental tiredness.
How do you fix brain fog?
Find the cause first. Protect your sleep, move every day, eat and drink regularly, cut back on alcohol and manage stress. If it lasts weeks, ask your GP about blood tests for iron, B12, folate and thyroid.
What is the best supplement for brain fog?
There isn’t one for everyone. Iron or vitamin B12 help if a blood test shows you’re low. Otherwise, sleep, movement and regular meals do more than any supplement.
What are the best supplements for menopause brain fog?
No supplement is proven to clear menopause brain fog. HRT can help with menopause symptoms, and protecting sleep makes a big difference. Talk to your GP about your options.
When is brain fog serious?
Get urgent help if confusion comes on suddenly, or with slurred speech, weakness on one side or a severe headache. See a GP if brain fog lasts weeks, gets worse or affects daily life.
How long does brain fog last?
It depends on the cause. Brain fog from a few bad nights usually lifts within days, while after an illness such as COVID it can take weeks or months. If it lasts more than a few weeks without a clear reason, see your GP.
Is it brain fog or ADHD?
ADHD is a lifelong pattern, with symptoms that usually start before the age of 12. Brain fog is usually a newer change, often linked to sleep, stress, illness or hormones. Only a specialist can diagnose ADHD, so talk to your GP if you’re unsure.
Is brain fog a sign of dementia?
Usually not. Forgetting words or names now and then is common, and memory problems can be caused by stress, anxiety, depression or poor sleep. See a GP if memory problems are getting worse or affecting daily life.
Sources
- Wilson JC et al (2025). Brain fog with long covid and chemotherapy: systematic review and meta-analysis. BMJ Mental Health.
- Lim J, Dinges DF (2010). A meta-analysis of the impact of short-term sleep deprivation on cognitive variables. Psychological Bulletin.
- Huang Z et al (2026). Effect of breaking up prolonged sitting with physical activity on executive function: a three-level meta-analysis. International Journal of Behavioral Nutrition and Physical Activity.
- NHS. Menopause symptoms.
- NHS. Long COVID.
- NHS. Underactive thyroid (hypothyroidism).
- NHS. Overactive thyroid (hyperthyroidism).
- NHS. Vitamin B12 or folate deficiency anaemia.
- NHS. Iron deficiency anaemia.
- Belenky G et al (2003). Patterns of performance degradation and restoration during sleep restriction and subsequent recovery: a sleep dose-response study. Journal of Sleep Research.
- NHS. ADHD in adults.
- NICE (2018). Attention deficit hyperactivity disorder: diagnosis and management (NG87).
- NHS. Memory loss (amnesia).
- NHS. What is dementia?
- NHS. Symptoms of dementia.
This guide is general information, not medical advice. Evopure makes the Magnesium Glycinate Sleep Complex and Flow CBD Oil.
