Medically reviewed by Shahrzad Shadmani, PMHNP-BC, FNP-C, founder of Integrative Psychiatry and Wellness (IPW Health).
Published September 16, 2026.
You reread the same paragraph three times. A word you use every day will not come when you need it. You walk into a room with a clear purpose and arrive with none. At work you get through the day, but it takes everything you have, and you are not sure anyone else is working this hard to stay present in a meeting.
People call this brain fog. It is a good description of the experience. It is not an explanation of it, and treating it as one is how people end up in the wrong place for a long time.
Brain fog is a symptom, not a diagnosis
There is no diagnostic code for brain fog and no test that confirms it. It is an everyday term for a cluster of experiences: slowed thinking, trouble holding attention, difficulty retrieving words, a sense that recall takes effort it did not used to take.
That matters because symptoms have differentials and diagnoses have treatments. “Brain fog” tells a clinician what you are experiencing. It tells them nothing yet about why.
The list of things that cause it is long
Here is the differential a clinician is actually working through:
Sleep. The most common cause, and the most commonly skipped. Insufficient sleep, fragmented sleep, shift work, and untreated obstructive sleep apnea all produce exactly this picture. Sleep apnea in particular is underdiagnosed, is not limited to people who snore loudly or carry excess weight, and is treatable.
Depression. Cognitive symptoms are part of depression, not a side note to it. Concentration difficulty and slowed thinking appear in the diagnostic criteria. Some people experience the cognitive changes more prominently than sadness, which is one reason depression gets missed in people who describe their problem as fog.
Anxiety. Attention is a finite resource. When a substantial share is committed to monitoring for threat, less is available for the task in front of you.
ADHD. Frequently identified in adulthood, particularly in women, and particularly when demands rise or previously effective coping strategies stop working. Inattentive-presentation ADHD is often described by the person experiencing it as fog rather than as a focus problem.
Thyroid disease. Hypothyroidism slows thinking; hyperthyroidism scatters it. Both are common, both are detected by a blood test, both are treatable.
Anaemia and nutritional deficiency. Iron deficiency — with or without anaemia — and B12 deficiency both cause fatigue and cognitive complaints, and both are easy to test for.
Perimenopause. Cognitive complaints are commonly reported during the menopause transition, and research using objective testing has found measurable but generally modest changes in some domains during this period. Sleep disruption from night sweats is a major contributor and is separately treatable.
Medications. Anticholinergics, sedating antihistamines, benzodiazepines, some anticonvulsants and mood stabilisers, opioids, sleep medications and alcohol all affect cognition. Bring your full list, including over-the-counter products and supplements, to any evaluation.
Post-viral states. Cognitive symptoms following COVID-19 and other infections are well documented and can persist. Research is active and the mechanisms are not settled.
Chronic pain and chronic illness. Persistent pain competes for attentional resources, and the inflammatory and autoimmune conditions that cause it are independently associated with cognitive complaints.
Why hormones get the blame
Hormones belong on that list. They are rarely the whole of it, and they are usually the first thing people land on anyway.
Part of the reason is timing. Fog often appears in the forties and fifties, alongside cycle changes, so the two get linked. But that decade also brings worsening sleep, peak caregiving and work demands, and rising rates of thyroid disease, depression and sleep apnea. Co-occurrence is not causation.
Part of it is commercial. “Your hormones are out of balance” is a saleable explanation with a product attached. “Let’s evaluate your sleep, screen you for depression and check your thyroid” is not. We have written separately about what hormones do and do not explain, including which tests are worth having.
And part of it is that the hormonal explanation feels better. It locates the problem outside your character and offers a fix. That instinct is sound — this is not a character problem. It just sometimes points at the wrong biology.
What a sensible workup looks like
A useful evaluation starts with history, not with tests: when it began, whether it came on gradually or suddenly, what makes it better or worse, how you are actually sleeping, what you are taking, how much alcohol is involved, and what else changed around the time it started.
Then screening for depression, anxiety and ADHD, and a review of whether symptoms track your menstrual cycle.
Then targeted labs — thyroid function, complete blood count, iron studies, B12, metabolic panel, vitamin D — ordered because something in the history pointed at them.
A sleep study when the history suggests apnea. Formal neuropsychological testing when the picture is unclear or the changes appear significant.
When to be seen sooner rather than reassured
Most brain fog is not a sign of a serious neurological condition. Some presentations should be evaluated promptly rather than watched:
- Cognitive change that came on suddenly, or over days rather than months
- Getting lost in familiar places, or difficulty with tasks you have done for years
- Other people noticing the change before you did, or being more concerned than you are
- Any accompanying neurological symptom — weakness, numbness, vision or speech change, new or severe headache, loss of coordination
- New confusion in an older adult, which can signal infection, medication effect or another acute cause
- Cognitive symptoms alongside hopelessness, or any thoughts of harming yourself
A sudden change in an older adult, or any of the neurological symptoms above, warrants urgent assessment rather than an appointment in three weeks.
On whether it gets better
This deserves a careful answer rather than a reassuring one.
What can honestly be said: when brain fog is driven by something treatable, treating it often helps. People whose sleep apnea is treated frequently report clearer thinking. Depression treatment often improves cognitive symptoms, though for some people they lag behind mood or persist. Correcting thyroid disease or a documented deficiency can help. Removing a medication that was contributing can help.
What cannot honestly be said is that any of this is guaranteed, or that it works on a timeline. Some people improve substantially. Some improve partially. Some find that a contributor is identified and treated and a degree of fog remains, which is worth naming rather than treating as a failure. The most reliable route to improvement is finding out what is actually driving it — not assuming you already know.
What to do next
Track it for a few weeks before your appointment: when it is worse, how you slept the night before, where you are in your cycle if you have one, what you took. That record will be more useful to a clinician than any single lab value.
Then get evaluated by someone who will work through the whole list rather than the first item on it.
At IPW Health we provide psychiatric evaluation, medication management and integrative psychiatric care by telehealth in California, Oregon, Washington and Colorado, and in person in Mission Viejo, California. We order and interpret the relevant laboratory work ourselves and complete adult ADHD evaluations in house; neuropsychological testing and sleep studies are arranged by referral.
This article is general education, not medical advice, and reading it does not create a patient–provider relationship. Treatment decisions depend on your history and should be made with a clinician who knows it.
If you are in crisis or having thoughts of harming yourself, call or text 988 to reach the Suicide and Crisis Lifeline, available 24 hours a day in the United States. If you are in immediate danger, call 911.
Sources
- American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, Text Revision (DSM-5-TR).
- National Institute of Mental Health. Depression; Attention-Deficit/Hyperactivity Disorder in Adults.
- National Heart, Lung, and Blood Institute (NIH). Sleep Apnea; Iron-Deficiency Anemia.
- National Institute of Diabetes and Digestive and Kidney Diseases (NIH). Hypothyroidism (Underactive Thyroid); Hyperthyroidism (Overactive Thyroid).
- National Institute of Neurological Disorders and Stroke. Dementia.
- Centers for Disease Control and Prevention. Long COVID.
- American College of Obstetricians and Gynecologists. The Menopause Years.
