“Brain fog” is not a diagnosis. It is a description: slow thinking, poor focus, forgetfulness, mental fatigue. It almost always has a cause, and the most common ones are fixable: poor sleep, stress, depression or anxiety, iron or B12 deficiency, thyroid problems, hormonal changes, long COVID, and medications.
The fastest route out is to find the cause, starting with a handful of simple blood tests. Lifestyle changes with real evidence (sleep, aerobic exercise) help almost everyone. Semax and Selank, two peptides developed in Russia, are the “nootropic peptides” people ask about; they have interesting animal and Russian clinical research, and no Western approval. Here is the full breakdown.
What brain fog feels like
People describe it in similar ways: reading the same paragraph three times, losing words mid-sentence, walking into a room and forgetting why, struggling to follow conversations, feeling mentally “slow” or “cloudy.” It often comes with physical fatigue. It is different from dementia: brain fog usually fluctuates, has an identifiable trigger, and improves when the cause is treated.
The 12 most common causes
| # | Cause | Clues |
|---|---|---|
| 1 | Sleep loss or poor-quality sleep | Short sleep, snoring, waking unrefreshed |
| 2 | Chronic stress | Overload, racing thoughts, tension |
| 3 | Depression | Low mood, loss of interest; poor concentration is a core symptom |
| 4 | Anxiety | Worry, restlessness; attention gets hijacked |
| 5 | Iron deficiency | Fatigue, heavy periods, pale skin, cold hands |
| 6 | Vitamin B12 deficiency | Numbness, tingling; common with vegan diets, metformin, acid blockers, older age |
| 7 | Thyroid problems | Weight change, feeling cold or hot, hair and skin changes |
| 8 | Perimenopause and menopause | Hot flashes, irregular periods, sleep disruption |
| 9 | Long COVID | Fog that began after a COVID infection, worse after exertion |
| 10 | Medications | Antihistamines, sleeping pills, benzodiazepines, some pain and bladder drugs |
| 11 | Blood sugar swings | Fog after large high-carb meals; diabetes or prediabetes |
| 12 | Alcohol and cannabis | Regular use, especially in the evening |
Others worth considering: ADHD (which many adults discover late), sleep apnea, dehydration, celiac disease, pregnancy, and cancer treatment (“chemo brain”).
The tests worth asking for
If brain fog has lasted more than a few weeks, ask your doctor about:
- Complete blood count (anemia)
- Ferritin (iron stores; can be low before anemia appears)
- Vitamin B12
- TSH (thyroid)
- Fasting glucose or HbA1c (blood sugar)
- Depending on symptoms: vitamin D, celiac screening, a sleep apnea assessment, a depression and anxiety screen, and a medication review.
These are standard, inexpensive and covered by provincial health plans when ordered by a physician or nurse practitioner.
What actually helps
Fix sleep first
Even modest sleep restriction measurably impairs attention and working memory, and people consistently underestimate how impaired they are. If you are sleeping under seven hours or waking unrefreshed, start here. See our guide to insomnia treatments that work.
Aerobic exercise
Regular aerobic exercise improves attention and executive function and increases BDNF, a growth factor that supports brain plasticity. Even a brisk 20-minute walk sharpens focus for the hours afterward.
Treat the underlying cause
Iron and B12 replacement, thyroid treatment, treating depression or anxiety, managing perimenopause (hormone therapy helps sleep and hot flashes for many), or adjusting a sedating medication often produce the biggest single improvement.
For long COVID: pacing
Long COVID brain fog often worsens after physical or mental overexertion (post-exertional malaise). Pacing activity, rather than pushing through, is the core strategy recommended by rehabilitation specialists.
Reduce cognitive load
Single-tasking, written lists, phone notifications off, and scheduling demanding work for your sharpest hours are low-tech and effective.
Supplements and nootropics: the evidence
| Option | Evidence | Notes |
|---|---|---|
| Caffeine | Strong (short-term alertness) | Costs sleep if taken late |
| Caffeine + L-theanine | Moderate | Smoother focus in small studies |
| Creatine | Moderate | Most benefit under sleep deprivation and in vegetarians |
| Omega-3 | Weak for healthy adults | Better if intake is low |
| Iron, B12, vitamin D | Strong if deficient | Little benefit if levels are normal |
| Ginkgo, “brain” blends | Weak | Mostly marketing |
Semax and Selank: what the research shows
Semax and Selank are short synthetic peptides developed at the Institute of Molecular Genetics of the Russian Academy of Sciences. Both are approved medicines in Russia and some neighbouring countries; neither is approved by Health Canada, the FDA or the European Medicines Agency.
Semax
Semax is a seven-amino-acid peptide based on a fragment of ACTH (the stress hormone signal), modified to last longer and remove hormonal activity. In Russia it is used after stroke and for some cognitive disorders. In rat studies, Semax increased levels of BDNF and its receptor in the hippocampus, a brain region central to memory (Dolotov et al., 2006). Human evidence comes mostly from Russian clinical studies that are hard to evaluate by Western standards. More in Semax side effects.
Selank
Selank is a seven-amino-acid analog of tuftsin, an immune peptide. In Russia it is used as an anti-anxiety agent, and it is described as calming without the sedation or dependence of benzodiazepines. Research has looked at its effects on GABA signalling and on the expression of genes involved in inflammation. Again, the human data are limited and mostly Russian. See common Selank research mistakes.
For a side-by-side comparison of mechanisms and research, read Selank vs Semax.
Neither peptide has been tested in Western controlled trials for brain fog, and neither is approved in Canada. If you are foggy, the causes and fixes above will help far more people, far more reliably, than any peptide.
| Research compound | Origin | From |
|---|---|---|
| Semax | ACTH(4–10) analog | $41 |
| Selank | Tuftsin analog | $40 |
Sold for laboratory research only, with independent testing in our COA library.
When to see a doctor urgently
- Sudden confusion, trouble speaking, facial droop or weakness on one side: call 911, as these can be signs of stroke.
- Fog after a head injury.
- Steadily worsening memory, getting lost in familiar places.
- Fog with fever, severe headache or a stiff neck.
FAQ
Tap a question to reveal the answer.
What causes brain fog?
Most often poor sleep, stress, depression or anxiety, iron or B12 deficiency, thyroid problems, hormonal changes such as perimenopause, long COVID, and sedating medications.
How do I get rid of brain fog fast?
In the short term, sleep, a brisk walk, hydration and caffeine help. For lasting improvement, identify and treat the underlying cause, starting with basic blood tests.
What blood tests check for brain fog?
A complete blood count, ferritin, vitamin B12, TSH and blood sugar (glucose or HbA1c) are the usual starting tests.
Can low iron cause brain fog?
Yes. Iron deficiency, even before full anemia, is linked to fatigue and poor concentration, especially in people with heavy periods.
Does Semax help brain fog?
It has not been tested for brain fog in Western controlled trials. Animal studies show it increases BDNF in the hippocampus, and it is approved in Russia for some neurological uses, but not in Canada.
Is brain fog a sign of dementia?
Usually not. Brain fog tends to fluctuate and have a clear cause. Steadily progressive memory loss, especially getting lost or struggling with daily tasks, needs a medical assessment.
Related reading
References
- Dolotov OV, Karpenko EA, Inozemtseva LS, et al. Semax, an analog of ACTH(4-10) with cognitive effects, regulates BDNF and trkB expression in the rat hippocampus. Brain Res. 2006;1117(1):54–60. PubMed
- Health Canada. Post COVID-19 condition (long COVID). Government of Canada
This article is general information, not medical advice. TrueLabs research compounds are sold for in vitro and laboratory research use only and are not intended for human or veterinary use.