Brain fog: causes, red flags and when to get it checked

Attention and working memory depend on sleep, mood, hormones, blood sugar and a healthy supply of nutrients and oxygen to the brain. Disrupting any of these makes thinking feel slow. Inflammation after infection may also play a role in post-viral brain fog.

• Poor or insufficient sleep, including sleep apnoea, and shift work.

• Stress, anxiety, burnout and depression.

• Perimenopause and menopause, with hormone shifts affecting memory and concentration.

• Medicines: antihistamines, sedatives, anticholinergics, some antiepileptics, beta blockers and opioids; also alcohol and cannabis.

• Iron deficiency, anaemia, vitamin B12 or D deficiency, and dehydration.

• Underactive thyroid, diabetes (high or low sugar), kidney and liver disease.

• Post-viral states, long COVID and chronic fatigue syndrome.

• Dementia, brain injury, multiple sclerosis, tumours and infections, which usually have other features.

Progressive worsening over weeks to months, memory loss affecting daily tasks, getting lost, personality or behaviour change, severe or new headaches, vision changes, weakness, speech difficulty, seizures, confusion, and symptoms after head injury warrant urgent assessment.

• Call 999: sudden confusion, slurred speech, facial droop or weakness.

• Same-day GP or NHS 111: new confusion with fever, severe headache or after a head injury.

• GP within weeks: brain fog lasting more than a few weeks with other symptoms, or progressive memory problems.

• Routine: brain fog during a stressful, sleep-deprived period that improves with rest.

The doctor asks when it started, severity, sleep, mood, stress, menopause symptoms, alcohol, drugs, medicines, diet, infections including COVID, and effects on work and life. They carry out a cognitive screen if indicated, check blood pressure, weight, thyroid and neurological function.

• Blood tests: full blood count, ferritin, B12, folate, vitamin D, thyroid function, glucose or HbA1c, kidney, liver and calcium.

• Screening questionnaires for depression, anxiety and sleep problems.

• Cognitive screening tests: if memory loss is a concern.

• Sleep study: if sleep apnoea is suspected.

• MRI or CT brain: for red flags or progressive symptoms.

Prioritise seven to nine hours of sleep, regular exercise, balanced meals, hydration and reduced alcohol. Break tasks into steps, use lists and calendars, and take breaks. For menopause, discuss treatment options with a GP. Pace activity if post-viral fatigue is present. Avoid unproven supplements and "detox" regimes.

The NHS route is a GP, with memory services, neurology or long COVID clinics as needed. Private GP, neurology and menopause services offer direct access to testing and treatment.