What helps
How to clear brain fog
There is no single cure because brain fog is not one thing. But there is a process that works for most people - a sequence of increasingly specific steps that narrows down what's actually going on.
Phase 1 · This week
Fix the foundation
Free. No doctor needed. These aren't the whole answer but they're the floor everything else is built on. Ignoring them while chasing exotic explanations is backwards.
Sleep
Your brain clears metabolic waste during deep sleep through the glymphatic system. In the mouse study that identified this system, interstitial space expanded by roughly 60% during sleep, allowing cerebrospinal fluid to flush waste products (Xie et al., Science 2013). Human imaging has since confirmed analogous processes. Consistent wake time, 7-9 hours, no screens before bed, cool dark room. If you snore or wake unrested despite enough hours, request a sleep study - sleep apnea is dramatically underdiagnosed.
⏱ 1-2 weeks for noticeable change
Hydration
Just 2% dehydration impairs performance in tasks requiring attention, psychomotor skills, and immediate memory - the exact cognitive functions brain fog affects (Adan, J Am Coll Nutr 2012). A meta-analysis of 33 studies confirmed dehydration consistently impairs cognitive performance across age groups (Wittbrodt & Millard-Stafford, Med Sci Sports Exerc 2018). 2+ litres daily. Front-load before afternoon. Add more if you drink coffee, exercise, or live in a hot climate.
⏱ Days
Blood sugar
Protein at every meal, especially breakfast. 20-25g minimum. Breakfast macronutrient composition significantly influences executive function - specifically, a protein-rich breakfast improved cognitive performance compared to a high-carb or skipped breakfast (Brandley & Holton, Am J Health Promot 2020). If you crash 2-3 hours after meals with irritability and fog, reactive hypoglycaemia is worth investigating.
⏱ Same day if blood sugar is a factor
Movement
30 minutes of moderate-to-vigorous exercise increases BDNF (brain-derived neurotrophic factor) by 20-40% - BDNF supports neuroplasticity and the formation of new neural connections (Schmolesky et al., J Sports Sci Med 2013). During prolonged exercise, the brain itself contributes 70-80% of the circulating BDNF increase (Rasmussen et al., Exp Physiol 2009). Not about fitness. About giving your brain the chemical signals it needs to repair and connect.
⏱ 1-2 weeks cumulative
Phase 2 · Book these tests
Get the right blood work
Not generic blood work. These 6 specific tests catch a disproportionate share of treatable causes. If your doctor has run a "basic metabolic panel" and said everything is fine, that panel likely did not include these markers.
TSH + Free T4
Thyroid dysfunction is one of the most common and most underdiagnosed causes of brain fog. TSH alone can miss subclinical hypothyroidism.
▼
TSH + Free T4
Thyroid dysfunction is one of the most common and most underdiagnosed causes of brain fog. TSH alone can miss subclinical hypothyroidism.
Optimal TSH is debated - many endocrinologists consider 0.5-2.5 more appropriate than the lab range of 0.5-4.5. If TSH is borderline, ask for Free T3 and thyroid antibodies (TPO, TgAb) as well.
Ferritin
Iron storage. Lab "normal" starts at 12-15, but neurological symptoms including brain fog often persist until ferritin reaches 45+. Iron is a cofactor for the enzymes that produce dopamine and serotonin.
▼
Ferritin
Iron storage. Lab "normal" starts at 12-15, but neurological symptoms including brain fog often persist until ferritin reaches 45+. Iron is a cofactor for the enzymes that produce dopamine and serotonin.
Not the same as haemoglobin. You can have "normal" haemoglobin while your iron stores are depleted. Ask specifically for ferritin.
Vitamin B12
Essential for myelin maintenance and neurotransmitter synthesis. Common deficiency in vegetarians, vegans, older adults, and people on PPIs or metformin.
▼
Vitamin B12
Essential for myelin maintenance and neurotransmitter synthesis. Common deficiency in vegetarians, vegans, older adults, and people on PPIs or metformin.
If B12 is low-normal (200-400 pg/mL), methylmalonic acid (MMA) is a more sensitive marker. Serum B12 can look adequate while functional B12 is insufficient.
Vitamin D
Vitamin D receptors are concentrated in the prefrontal cortex and hippocampus - the brain regions most involved in focus, memory, and executive function. Lab "sufficient" is 30 ng/mL, but optimal for cognition appears to be 40-60.
▼
Vitamin D
Vitamin D receptors are concentrated in the prefrontal cortex and hippocampus - the brain regions most involved in focus, memory, and executive function. Lab "sufficient" is 30 ng/mL, but optimal for cognition appears to be 40-60.
Extremely common deficiency in northern latitudes, people with darker skin, people who work indoors, and older adults. Winter levels can be dramatically lower than summer.
Fasting glucose
Rules out diabetes and pre-diabetes, both of which cause cognitive symptoms. If normal but you suspect blood sugar crashes, HbA1c gives a 3-month average. A continuous glucose monitor (CGM) for 2 weeks gives the most granular picture.
▼
Fasting glucose
Rules out diabetes and pre-diabetes, both of which cause cognitive symptoms. If normal but you suspect blood sugar crashes, HbA1c gives a 3-month average. A continuous glucose monitor (CGM) for 2 weeks gives the most granular picture.
Complete blood count (CBC)
Screens for anaemia, infection markers, and basic blood health. Not brain-fog-specific but catches obvious problems that could be contributing.
▼
Complete blood count (CBC)
Screens for anaemia, infection markers, and basic blood health. Not brain-fog-specific but catches obvious problems that could be contributing.
Phase 3 · The detective work
Look at the pattern
Many causes don't show up in blood work. They're diagnosed by timing, triggers, and what travels with the fog. These five questions narrow the field dramatically.
When did it start?
Sudden (days) → post-viral, medication, head injury. Gradual (months) → nutritional, hormonal, sleep disorder. Lifelong → ADHD, undiagnosed sleep apnea, chronic anxiety.
What makes it worse?
After meals → blood sugar. After exertion → ME/CFS, POTS. Standing up → POTS, orthostatic hypotension. Stress → anxiety, burnout. Specific building → mould, air quality.
What makes it better?
Rest → sleep deficit. Eating → blood sugar. Lying down → POTS. Exercise → depression, sedentary. Leaving a building → environmental exposure.
What time of day is worst?
Morning → sleep disorder, sleep apnea. Afternoon → blood sugar crash. Evening → ADHD exhaustion, medication wearing off. Typically, the same → thyroid, nutritional deficiency.
What else changed?
Fatigue, weight, temperature sensitivity, digestion, hair loss, mood, menstrual changes, joint pain - companion symptoms are often more diagnostic than the fog itself. Write them all down.
Phase 4 · The specific causes
Investigate the causes that match
Most people have 2-3 contributing factors, not one dramatic diagnosis. Fixing one thing rarely solves everything. Fixing three things at moderate levels often produces dramatic improvement. Each cause page covers the mechanism, relevant tests, evidence-graded research, and practical next steps.
Browse all 66 causesPhase 5 · Make the pattern visible
Track what changes
One variable at a time. Two weeks minimum before evaluating. A daily note - fog severity 1-10, hours of sleep, what you tried, anything notable - makes the pattern visible within 2-3 weeks. This data also transforms your next doctor's appointment from "I feel foggy" to "here's what I've tracked."
Pattern journal →What not to do
Buy a stack of supplements from Reddit. One variable at a time. Two weeks minimum before evaluating. If you start five things at once, you won't know which one helped.
Self-diagnose from a single cause page without blood work. The most common causes are metabolic and testable. Get the data first.
Skip the basics because they're boring. Sleep, hydration, blood sugar, and movement are the foundation everything else is built on. Fix them first.
Wait for it to be 'bad enough' to investigate. If it's affecting your work, relationships, or quality of life, it's already worth investigating.
Accept 'it's just stress' without blood work. It might be stress. It might be thyroid disease with a TSH of 6.2 that nobody tested for. Both are treatable. Only one shows up in blood.
The framework in one paragraph
Fix sleep, water, blood sugar, and movement first. Get thyroid, iron, B12, D, glucose, and CBC tested. While waiting for results, track your fog pattern - when it starts, what makes it worse, what makes it better, and what other symptoms travel with it. Compare that pattern against the causes that fit. Investigate the top 2-3. One change at a time. Two weeks minimum. Your brain is a system under pressure from multiple directions. Reduce enough pressures to get below the threshold where clear thinking stops being available.