For many people with Long COVID, the infection itself was only the beginning. Weeks or months later, they found themselves struggling with tasks that once felt automatic — following a conversation, remembering a name, finding the right word, staying focused through a workday.
People quickly called this condition brain fog.
But brain fog was never a diagnosis to begin with — it was a description, a label for something people can feel but can’t point to. Research aims to figure out what sits underneath the label, and whether the same answer applies to everyone carrying it, or just some of them.
A Barrier Under Scrutiny
One serious line of research involves the blood-brain barrier — the selective layer that decides what’s allowed to move from the bloodstream into brain tissue. In a 2024 study, researchers found evidence of blood-brain barrier disruption alongside sustained systemic inflammation in a group of people with Long COVID-associated cognitive impairment.
That’s a plausible bridge between what’s happening in the blood and what shows up in the brain. It is not proof that barrier disruption explains every case of brain fog. The study was relatively small, and Long COVID is a big enough, varied enough condition that one result doesn’t get to close the book on it.
Other research is looking at immune dysregulation, small-vessel problems, autonomic dysfunction, sleep disturbance, metabolic changes, and lingering viral material. These mechanisms overlap in the same person. They may also carry different weight from one patient to the next — which is a polite way of saying nobody has found the one true answer yet.
What About Persistent Spike Protein?
Studies have detected viral proteins, or other signs of viral persistence, in some people well after the acute infection has cleared. Researchers are still working out whether those findings contribute to symptoms and, if so, in whom.
Nattokinase is one ingredient researchers are looking into. It’s an enzyme pulled from natto, the fermented soybean dish, and in a lab study it degraded SARS-CoV-2 spike protein sitting in cell lysates. However, it was not a trial conducted in people.
Other Ingredients Often Discussed for Cognitive Support
A handful of ingredients come up constantly in brain-health conversations, and each deserves a straight answer rather than a shrug. Omega-3 fatty acids include EPA and DHA, and DHA genuinely is a structural building block of the brain — that much is real chemistry. That doesn’t prove an omega-3 supplement treats Long COVID brain fog specifically — evidence for cognitive benefit shifts depending on who’s being studied and what’s being measured — but it’s a start.
Ashwagandha also has decent evidence behind it for stress and sleep.
Green tea contains caffeine and plant compounds, including catechins. A cup might sharpen alertness for some people, because caffeine is a stimulant and that’s what stimulants do; it might just as easily worsen sleep, anxiety, palpitations, or postural symptoms for someone whose autonomic system is already unhappy.
Brain fog was never a diagnosis to begin with — it was a description, a label for something people can feel but can’t point to. Research aims to figure out what sits underneath the label, and whether the same answer applies to everyone carrying it, or just some of them.
None of these has earned the title of cure for Long COVID brain fog, and none should be mistaken for the actual work below — which is where the real gains tend to live. Anyone who tries one anyway is better off changing a single variable at a time; it’s the only way to tell what helped from what happened alongside it.
What Can Help Now
Clinical care starts by ruling out impostors—conditions that can mimic or amplify cognitive symptoms on their own, including anemia, thyroid disease, vitamin deficiencies, sleep apnea, medication effects, depression, anxiety, hearing or vision changes, and other neurological conditions. Whatever the evaluation actually finds is what gets treated — not a guess about spike protein, and not a hopeful stack of supplements.
In the meantime, practical strategies can lighten the daily load while the science keeps developing. Written reminders, fewer tasks running at once, scheduled breaks, consistent sleep timing, and pacing that accounts for mental effort as seriously as physical effort all help conserve cognitive energy that’s already in short supply. Speech-language or occupational therapy can help build individualized strategies for memory, attention, and the actual demands of a working day.
Sudden confusion, weakness on one side of the body, trouble speaking, a severe new headache, fainting, or chest pain are not brain-fog symptoms to wait out. It needs urgent medical attention. Long COVID should never become a label of convenience for every new thing that goes wrong.
The Honest State of the Science
Researchers have moved well past asking whether post-COVID cognitive symptoms are real. The harder questions now are about subtypes, mechanisms, biomarkers, and treatments — and the answers are arriving, just not all at once, and not in a single file.
Brain fog is an untidy problem wearing a tidy name. Progress starts by taking the symptoms seriously and the evidence precisely — in that order, without skipping either one.
Educational note
This article is for general educational purposes only. It is not medical advice and does not replace care from a qualified health professional.
References
Centers for Disease Control and Prevention. (2026, March 9). Signs and symptoms of Long COVID. https://www.cdc.gov/long-covid/signs-symptoms/index.html
Davis, H. E., McCorkell, L., Vogel, J. M., & Topol, E. J. (2023). Long COVID: Major findings, mechanisms and recommendations. Nature Reviews Microbiology, 21, 133–146. https://doi.org/10.1038/s41579-022-00846-2
Greene, C., Connolly, R., Brennan, D., Laffan, A., O’Keeffe, E., Zaporojan, L., O’Callaghan, J., Thomson, B., Connolly, E., Argue, R., Meaney, J. F. M., Martin-Loeches, I., Long, A., Ní Cheallaigh, C., Conlon, N., Doherty, C. P., & Campbell, M. (2024). Blood–brain barrier disruption and sustained systemic inflammation in individuals with long COVID-associated cognitive impairment. Nature Neuroscience, 27, 421–432. https://doi.org/10.1038/s41593-024-01576-9
National Center for Complementary and Integrative Health. (2025, February). Green tea. https://www.nccih.nih.gov/health/green-tea
