Brain Fog: Causes, What Helps and When to Check

What people mean by brain fog

"Brain fog" is a plain-language term for a range of symptoms that affect how clearly you think, focus, concentrate, remember and pay attention. [1] It is a term for a range of symptoms rather than a single diagnosis; a healthcare provider can look for the underlying cause. [1] It can show up as trouble concentrating, losing your train of thought, forgetfulness, not finding the right words, mental exhaustion or slow thinking. [1]

Because it describes symptoms, the useful question is what is behind it. This page is educational; it cannot diagnose you. Brain fog is not the same as mild cognitive impairment or dementia; see forgetfulness and memory loss if memory is your main concern.

Common contributors

One clinical overview lists several possible causes: [1]

• Lack of sleep (see Better Sleep and Insomnia).
• Stress, anxiety or depression (see Stress and relaxation).
• Hormonal changes, such as pregnancy or menopause (see Perimenopause and menopause).
• Medical conditions, including diabetes and low blood sugar, and autoimmune conditions such as lupus, multiple sclerosis and fibromyalgia.
• Poor nutrition, and neurodivergent conditions such as ADHD (ADHD in adults).
• Illness or treatment, including long COVID, chemotherapy and long hospital stays.

Medicines are a common and fixable contributor. Sleep and pain drugs are among the most common culprits; for example, over-the-counter sleep aids that contain diphenhydramine have anticholinergic properties, which are known to impair thinking in older people. [2] If you suspect a medicine, do not stop it on your own: track your symptoms for a week or two and share the notes with your doctor. [2] See Medicines, sleep, mood and illness that affect memory.

Two treatable medical causes deserve a mention. An underactive thyroid can cause difficulty concentrating or thinking clearly, [3] and vitamin B12 or folate deficiency can cause problems with memory, understanding and judgment, and some problems can become irreversible if treatment is delayed. [4] See thyroid and fatigue and vitamin B12 deficiency. A blood test is how these are checked.

Brain fog after illness or long COVID

The NHS lists long COVID symptoms, and care teams may include cognitive rehabilitation, which uses activities to improve memory, concentration, thinking and mood, along with help for fatigue and CBT for anxiety, depression and fatigue. [5] A 2024 BMJ living systematic review of 24 trials found moderate-certainty evidence that an online CBT program probably improves concentration compared with usual care. [6] Evidence for other treatments was less certain, and we did not find a reliable evidence summary supporting supplements for post-illness brain fog (proper evidence not found).

What tends to help

There is no specific treatment for brain fog itself; care depends on the cause. [1] Clinicians often start with general steps: improve sleep habits, eat regular nutritious meals, get daily physical activity, write down important information, take short breaks through the day and consider CBT. [1] These are sensible habits rather than proven cures for brain fog; the strength of evidence varies by cause. See Focus habits and Brain-healthy habits.

Supplements. We did not find evidence that any "brain fog" supplement works. For what is known about memory supplements, read nootropics and memory supplements and check how interactions work first.

Caffeine and mental fatigue. Caffeine can be part of a healthy diet for most people, but too much can have negative effects; sensitivity varies. [7] See caffeine and energy drinks.

When to check

Contact a healthcare provider if brain fog is interfering with your quality of life or does not clear. [1] See a doctor if memory problems affect daily life, because treatable causes are common. [8]

Sudden confusion is different: it needs urgent help. See when to get help.