Last updated: October 2026
Brain fog is a common term for feeling mentally slow, forgetful, unfocused or “cloudy”. It isn’t a medical diagnosis but a symptom. The most common causes are poor sleep, stress, menopause, long COVID, low mood, dehydration and some medicines, plus deficiencies such as low iron or vitamin B12. Better sleep, movement and regular meals help most people.
Below: brain fog symptoms, common causes and what to do about each, quick fixes for a foggy day, supplements, and when to see your GP.
Brain fog symptoms
- 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.
What causes brain fog?
| Cause | Clues | What helps |
|---|---|---|
| Poor or short sleep | Worse after bad nights | A regular schedule. A meta-analysis found sleep loss hits attention hardest. See sleep hygiene |
| Stress and burnout | Overloaded, wired but tired | See burnout symptoms |
| Menopause and perimenopause | Mid-life, with hot flushes or irregular periods | 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 | A GP blood test. See why am I always tired? |
| Thyroid problems | Weight change, feeling cold or hot | A GP blood test |
| 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.
How to clear brain fog
- 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.
- Get outside in daylight every day.
Quick fixes for a foggy day
- 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
Supplements for brain fog
Supplements help most when they fix a deficiency, such as iron or vitamin B12, confirmed by a blood test. Magnesium contributes to normal psychological function and to the reduction of tiredness and fatigue. 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.
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.
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.
This guide is general information, not medical advice. Evopure makes the Magnesium Glycinate Sleep Complex and Flow CBD Oil.
