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Long COVID Brain Fog and Serotonin: What the 2023 Study Behind the Viral Reel Shows
An Instagram reel says Long COVID brain fog comes from gut damage and low serotonin, and that serotonin-boosting treatments restored thinking in mice. The study is real, and its mouse results are early. No treatment is proven for Long COVID brain fog.
Original commentary from the Cancer Explained editorial team.
Please note: this page is educational only — it is not medical advice, and it does not speculate about anyone’s health beyond reliable public reporting. For questions about your own health, talk with your healthcare team.
What the post claims
An Instagram reel from the account @what.ai.unlocked describes a 2023 study in the journal Cell about Long COVID and "brain fog." It says the virus damages gut cells that make serotonin, that this lowers the amount of an amino acid called tryptophan the body absorbs, and that this disrupts a nerve called the vagus nerve and so harms thinking. It says an estimated 65 million people have Long COVID. It also says serotonin-boosting treatments, including SSRIs, tryptophan and restoring gut bacteria, partly restored thinking in mice, and that human trials are now underway.
This is not a cancer story. We looked at it because brain fog is also a common worry during and after cancer treatment, and posts like this one travel fast.
The study behind the reel
The paper is Wong and colleagues, "Serotonin reduction in post-acute sequelae of viral infection," published in Cell on October 26, 2023 (PubMed 37848036). The opening of its abstract says people with Post-Acute Sequelae of COVID-19 (PASC, or Long COVID) show lower serotonin, and that viral infection and inflammation can reduce serotonin. The full paper was blocked to us, so we did not read the methods, the number of people studied or the mouse experiments ourselves. What the reel says about the mouse results, and what we found in summaries of the paper, is that restoring serotonin in mice with SSRIs or serotonin precursors reversed memory problems.
So the study is real and published in a major journal. What it describes is a possible explanation that fits mouse experiments and measurements in people. It is not a proven cause of brain fog in people, and it is not a treatment.
What is known about treatment
We could open one federal source on treatment: the NIH-funded RECOVER program. In November 2025 it reported results of RECOVER-NEURO, a trial of 328 adults at 22 U.S. sites that tested three non-drug approaches for cognitive symptoms of Long COVID: online brain training, brain training with a cognitive rehabilitation program, and brain training with a brain-stimulation cap. All groups improved a little, and none did better than the others. The lead researcher said, "None of our rehabilitation approaches to treatment for cognitive Long COVID proved to be effective." The trial was published in JAMA Neurology. RECOVER called it one of the first NIH-funded trials to study any treatment for people with cognitive symptoms after a SARS-CoV-2 infection.
We did not find a source showing that SSRIs, tryptophan or gut bacteria treatments work for Long COVID brain fog in people. The reel's line that human trials are underway may be true, but we could not confirm it, and a trial being underway is not a result.
About the "65 million" figure
The figure comes from a 2023 review by Davis and colleagues in Nature Reviews Microbiology, which estimated that at least 65 million people worldwide have Long COVID. We saw this only as a citation in search results and did not open the review. It is an estimate, not a count, and estimates vary with how Long COVID is defined.
What this means
- A study explaining brain fog in mice is a lead for researchers, not advice for patients.
- Nothing we opened says people should take an SSRI or tryptophan supplement for brain fog. Those are medicines and supplements to discuss with your own doctor, not to start because of a reel.
- A short reel cannot show how strong the evidence is. Our guide to spotting misinformation online lists questions to ask about a claim like this.
A note for people in cancer treatment
Brain fog during or after cancer treatment ("chemo brain") has different causes and different options. Our pages on cancer-related brain fog and chemo brain: what helps and what to ask cover that. Talk to your care team about new confusion, trouble thinking or memory changes, because some causes, such as infection, low sodium or medicine side effects, are treatable. Call 911 or go to an emergency room for sudden confusion, a severe headache, weakness on one side or trouble speaking.
Sources
- PubMed, Wong et al., "Serotonin reduction in post-acute sequelae of viral infection," Cell, 2023: pubmed.ncbi.nlm.nih.gov (only the opening of the abstract could be read)
- NIH RECOVER, "RECOVER-NEURO clinical trial shares results of three non-drug treatments for cognitive symptoms of Long COVID": recovercovid.org
- National Cancer Institute, "Cognitive Impairment in Adults with Cancer (PDQ)": cancer.gov
- Instagram reel from @what.ai.unlocked (the claim being checked): not linked here
How this article was prepared
An AI-assisted editorial system helped prepare this page. It used the public Instagram post, PubMed and RECOVER pages. The full Cell paper and the 65 million review were not opened. No named medical reviewer has reviewed it unless one is listed.
Cancer Explained is published by the National Cancer Information Foundation. It is not medical advice and does not suggest a test or treatment.
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Put the story in context
Prevention, possible warning signs, screening, and diagnosis
This story relates to Brain fog (cognitive symptoms) and a viral post about Long COVID. The information below is general: it does not reveal anything else about a public person’s health, and not every point applies to every cancer. Personal advice depends on age, symptoms, family history, exposures, and medical history.
Prevention and risk reduction
Not every cancer can be prevented. Avoiding tobacco, protecting skin from ultraviolet radiation, limiting alcohol, staying active, and receiving recommended HPV or hepatitis B vaccination can lower the risk of certain cancers. A risk factor is not a prediction or a cause in one individual.
Symptoms and possible early signs
Possible signs vary and are often caused by conditions other than cancer. Changes worth discussing include a new lump, unexplained bleeding or weight loss, a persistent cough, lasting bowel or bladder changes, a changing skin spot, or symptoms that persist or worsen. Some early cancers cause no symptoms.
Screening and early detection
Screening looks for certain cancers before symptoms begin. Recommended tests exist only for some cancers and depend on age and risk. Screening can have benefits and harms; it is not the same as evaluating a new symptom, and there is no single routine scan or blood test that reliably screens for every cancer.
How cancer is diagnosed
Diagnosis may involve a history and exam, imaging, laboratory tests, and often a biopsy. Pathology can identify the cancer type and may test biomarkers that guide treatment. Symptoms, screening results, tumor markers, or online stories alone cannot confirm cancer.
A public story may encourage questions, but it should not be used to estimate your risk or choose testing. Contact a healthcare professional about a persistent or concerning change. Seek urgent care for severe or rapidly worsening symptoms.