What causes brain fog, and what helps
Brain fog isn't a diagnosis, but it's real. Here's what it feels like, what usually causes it, what helps clear it and when to see your GP.
- Written by
- George M.
- Last updated
- Reading time
- 8 min read
Overview
Brain fog is an everyday term for slow thinking, forgetfulness and poor focus, not a medical diagnosis. It's usually caused by poor sleep, stress or lifestyle, and sometimes by hormone changes, illness, medicines or low B12. Better sleep and regular movement help most. See a GP if it lasts for weeks.
Key points
- Brain fog is a word for a mix of symptoms, not one condition or a diagnosis.
- Forgetfulness and trouble concentrating are what people describe most often.
- Poor sleep, stress and lifestyle are the usual causes, and menopause, medicines or low B12 less often.
- Protecting your sleep helps, and a single bout of exercise gives thinking a small, quick boost.
- See a GP if you've been tired for a few weeks and don't know why.
What is brain fog?
Brain fog is a word people use for a mix of symptoms, such as slow thinking, forgetfulness and trouble concentrating. It isn't a medical term or a diagnosis, but it is a very real problem [1].
Because it isn't one thing, it doesn't have one cause. Neurologists who studied how people describe brain fog found the term covers "not one single experience", but a range of different ones [2]. Working out what's behind yours is the first step to clearing it.
So treat this guide as a checklist. Rule out the easy causes first, then start with one change today.
What does brain fog feel like?
Most often, like forgetting things and struggling to focus. In a study of 141 first-hand descriptions of brain fog posted online, these were the most common [2].
| What people described | Share of descriptions |
|---|---|
| Forgetfulness | 36% |
| Difficulty concentrating | 30% |
| Feeling detached or unreal | 24% |
| Slow thinking that takes effort | 18% |
| Difficulty communicating | 16% |
| A fuzzy feeling or pressure in the head | 7% |
Many people described more than one, so the shares add up to more than 100%. About half of all the posts the researchers collected came from online groups about illness, so they may not reflect everyone's brain fog.
What causes brain fog?
Usually something everyday, such as poor sleep or stress. NHS Wales says there's a strong link between brain fog and fatigue, poor sleep, depression, anxiety and stress [1]. Less often, it's a sign of something your GP can test for and treat.
| Cause | What to know |
|---|---|
| Poor or short sleep | Even one short night makes you sleepier and slows your attention [3] |
| Stress | Difficulty concentrating and being forgetful are both signs of stress [4] |
| Lifestyle | An unhealthy diet and little exercise are common causes of tiredness [5] |
| Hormone changes | Perimenopause and menopause can bring problems with memory and concentration [6] |
| Illness | Infections such as COVID-19 and glandular fever can leave you tired [5] |
| Medicines | Some medicines and treatments cause tiredness, and sedating ones can leave you foggy [2][5] |
| Low vitamin B12 | Can cause problems with memory, understanding and judgement [7] |
| Anaemia, diabetes or thyroid | A GP may do blood tests for these if you've been tired for weeks [5] |
Can stress cause brain fog?
Yes. The NHS lists difficulty concentrating, struggling to make decisions, feeling overwhelmed and being forgetful among the mental signs of stress [4].
Stress can also change how you sleep, drink or smoke, which can make the fog worse. The NHS suggests not using alcohol or cigarettes to cope, and seeing a GP if you're struggling or what you're trying isn't helping [4].
How to get rid of brain fog
Start with the everyday causes, and pick one to work on this week. These are the changes with the best evidence behind them.
Protect your sleep
In a review of 44 studies, a single night of 2 to 6 hours' sleep made people sleepier and slowed their attention Strong [3]. The NHS suggests sticking to the same sleep times and avoiding caffeine, food and exercise in the couple of hours before bed [5]. If you struggle to drop off, try our guide to falling asleep fast.
Move, even briefly
A single session of exercise gives a small boost to attention, memory and planning skills straight afterwards. A 2025 review of 30 meta-analyses found this at every age and with every type of exercise studied Strong [8]. A brisk walk counts.
Eat well and go easy on alcohol
The NHS advice for tiredness is a healthy diet, regular exercise and not drinking too much alcohol [5]. Drink enough during the day too, and take short breaks from screens and long tasks.
Changes like these last longer when they become habits. Our guide to healthy habits that stick shows how to build them one small step at a time.
How long does brain fog last?
It depends on the cause. Fog from a short night usually lifts once you've slept well again, though more than one good night may be needed after a run of short ones.
Some causes last longer. Menopause symptoms usually last 7 to 9 years, and they can change during that time [6]. Low B12 needs treatment, because some of the problems it causes can become permanent if it's left untreated [7].
Menopause and brain fog
Problems with memory and concentration are a recognised symptom of perimenopause and menopause. The NHS says they may feel worse if you're also sleeping badly and feel very tired [6].
If you think your symptoms are down to the menopause, your GP can talk you through the options [6].
Do supplements help with brain fog?
We found no placebo-controlled trial of any supplement for brain fog itself. Vitamins such as B12 matter if you're low in them. A GP can check with a blood test, and low B12 is usually easy to treat with injections or tablets [7].
Ashwagandha and lion's mane are two plant ingredients that have been tested for memory and attention.
- Ashwagandha. In a trial of 120 adults aged 30 to 75 who reported problems with thinking and energy, 600 mg of ashwagandha root extract a day for 8 weeks improved memory and the accuracy of attention more than a placebo. The trial was funded by the maker of the KSM-66 extract Early [9].
- Lion's mane. In a pilot trial of 41 healthy adults aged 18 to 45, people were faster on one attention task an hour after a 1.8 g dose. Other results were mixed, and the authors called the findings tentative Early [10].
Our complete guides to ashwagandha and lion's mane cover the rest of the research, and what are nootropics? explains the wider group of ingredients.
When to see a GP
Where Nooroots fits
Nooroots Ashwagandha + Lion's Mane gives you 120 mg of KSM-66 ashwagandha and 500 mg of lion's mane extract in two caffeine-free capsules a day, for calm focus and calm resilience on demanding days.
It works alongside the basics in this guide, such as good sleep, regular movement and time to switch off.
Frequently asked questions
What does brain fog mean?
It's an everyday term for feeling slow, forgetful or unable to focus. It isn't a medical diagnosis, and it can have many causes [1].
Can low iron cause brain fog?
Low iron can lead to anaemia, which makes you tired and low on energy, and that can feel like brain fog. If you've been tired for weeks, a GP can check for anaemia with a blood test [5].
Can B12 deficiency cause brain fog?
Yes. The NHS lists problems with memory, understanding and judgement among the symptoms of low B12, and some can appear before anaemia develops [7]. It's more common in older people.
How do you clear brain fog quickly?
There's no instant fix, but moving helps. A single bout of exercise gives a small boost to attention and memory straight afterwards [8]. A walk outside, a glass of water and a break from screens are a good start.
Is brain fog permanent?
Rarely. Most brain fog lifts once the cause is dealt with. The main exception in this guide is low B12, which can cause lasting problems if it isn't treated, so it's worth getting checked [7].
Does lion's mane help with brain fog?
It hasn't been tested for brain fog itself. In one small trial in healthy young adults, people were faster on one attention task an hour after taking it [10].
References
Every study here is listed so you can read it yourself. This guide is for general information and doesn't replace advice from your GP or pharmacist. We review it when new research is published.
- Cwm Taf Morgannwg University Health Board (NHS Wales). Brain fog. Updated 20 October 2023. Accessed 17 October 2026. ctmuhb.nhs.wales
- McWhirter L et al. (2023). What is brain fog? Journal of Neurology, Neurosurgery and Psychiatry 94(4): 321–325. PMID 36600580
- Wüst LN et al. (2024). Impact of one night of sleep restriction on sleepiness and cognitive function: a systematic review and meta-analysis. Sleep Medicine Reviews 76: 101940. PMID 38759474
- NHS. Get help with stress. Page last reviewed 6 March 2026. Accessed 17 October 2026. nhs.uk/mental-health
- NHS. Tiredness and fatigue. Page last reviewed 2 June 2023. Accessed 17 October 2026. nhs.uk/symptoms/tiredness-and-fatigue
- NHS. Symptoms of menopause and perimenopause. Page last reviewed 19 May 2026. Accessed 17 October 2026. nhs.uk/conditions/menopause-and-perimenopause
- NHS. Vitamin B12 or folate deficiency anaemia. Page last reviewed 20 February 2023. Accessed 17 October 2026. nhs.uk/conditions/vitamin-b12-or-folate-deficiency-anaemia
- Chang YK et al. (2025). Effects of acute exercise on cognitive function: a meta-review of 30 systematic reviews with meta-analyses. Psychological Bulletin 151(2): 240–259. PMID 39883421
- Kale S, Lopresti A, Suri R, Garg N, Langade D (2024; in print 2026). Safety and efficacy of ashwagandha root extract on cognition, energy and mood problems in adults: prospective, randomized, placebo-controlled study. Journal of Psychoactive Drugs 58(1): 45–57. PMID 39498904
- Docherty S, Doughty FL, Smith EF (2023). The acute and chronic effects of lion's mane mushroom supplementation on cognitive function, stress and mood in young adults: a double-blind, parallel groups, pilot study. Nutrients 15(22): 4842. PMID 38004235
