Long COVID Brain Fog: Why It Happens and What Helps

Long COVID Brain Fog: What’s Really Going On in Your Brain

Long COVID brain fog happens because a SARS-CoV-2 infection can leave behind neuroinflammation, tiny fibrin microclots that block brain capillaries, and a leaky blood-brain barrier, and together these disrupt how neurons fire, communicate, and get fed oxygen and glucose. It affects an estimated 20 to 30 percent of people who develop long COVID, also called post-acute sequelae of SARS-CoV-2 (PASC) or post-COVID condition, according to Davis et al. (2023).

You can’t find the word you want. You walk into a room and forget why. You read the same paragraph three times and nothing sticks. Conversations feel like you’re listening through water. Tasks that used to be automatic now require conscious effort.

If this sounds familiar, and it started after a COVID-19 infection, you’re not imagining it. Brain fog is one of the most frequently reported symptoms of long COVID (also called post-acute sequelae of SARS-CoV-2, or PASC). It affects an estimated 20 to 30 percent of people who develop long COVID, and for many, it’s the symptom that most disrupts daily life.¹

The frustrating part is that “brain fog” isn’t a formal medical diagnosis. It’s an umbrella term for a cluster of cognitive symptoms: trouble concentrating, slow processing speed, word-finding difficulty, poor short-term memory, and mental fatigue. Clinicians and researchers also use terms like post-COVID cognitive impairment and neuro-PASC to describe the same picture. But just because the name is informal doesn’t mean the biology behind it is vague. We’re learning more every month about why this happens, and, more importantly, what can help.

Why COVID Causes Brain Fog: The Mechanisms

Brain fog after COVID isn’t caused by a single mechanism. It’s the result of several overlapping biological processes, and different patients may have different dominant drivers. Understanding these mechanisms matters because it affects which treatments are most likely to help. For a broader clinical overview of the condition itself, see our long COVID condition overview.

Neuroinflammation

SARS-CoV-2 triggers an intense immune response. In some people, that immune activation doesn’t fully resolve after the acute infection clears. Microglia, the brain’s resident immune cells, remain in an activated state, releasing pro-inflammatory cytokines that interfere with normal neuronal signaling. PET imaging studies have shown widespread neuroinflammation in long COVID patients, particularly in regions involved in attention and memory.²

Think of it like a fire alarm that keeps blaring after the fire is out. The brain’s immune system stays on high alert, and that chronic low-grade inflammation disrupts the delicate electrochemical environment neurons need to function properly.

Microclots and Impaired Microcirculation

One of the most significant discoveries in long COVID research is the presence of microclots, tiny, fibrin-rich clots that resist the body’s normal clot-dissolving mechanisms. These microclots were first identified by Dr. Resia Pretorius and colleagues at Stellenbosch University. They trap inflammatory molecules and can block capillaries throughout the body, including in the brain.³

When capillaries in the brain are partially blocked, neurons don’t get adequate oxygen and glucose. The result is cognitive sluggishness, a feeling that your brain is running on low battery. Microclots may also contribute to the exercise intolerance many long COVID patients experience, since muscles face the same microcirculation problems.

Blood-Brain Barrier (BBB) Disruption

The blood-brain barrier is a tightly regulated filtration system that controls what enters the brain from the bloodstream. COVID-19 can damage this barrier, allowing inflammatory proteins, immune cells, and other molecules to cross into the brain where they don’t belong. Studies using advanced MRI techniques have documented BBB leakage in long COVID patients with cognitive symptoms.⁴

A leaky blood-brain barrier means the brain is exposed to systemic inflammation it would normally be shielded from. This creates a vicious cycle: inflammation damages the barrier, which lets in more inflammatory molecules, which drives more neuroinflammation.

Viral Persistence

There’s growing evidence that SARS-CoV-2, or at least fragments of the virus (spike protein, viral RNA), can persist in tissues for months or even years after the initial infection. Viral proteins have been found in the gut, lymph nodes, brain tissue, and blood of long COVID patients long after they’ve “recovered.” This persistent viral material may continuously stimulate the immune system, keeping inflammation simmering.⁵

Autonomic Nervous System Dysfunction

Many long COVID patients develop dysautonomia, a malfunction of the autonomic nervous system that controls heart rate, blood pressure, digestion, and blood flow. When the autonomic system isn’t regulating blood flow properly, the brain may not receive adequate perfusion during activities that demand more oxygen. This can worsen cognitive symptoms, particularly when standing, concentrating, or multitasking. Dysautonomia frequently overlaps with postural orthostatic tachycardia syndrome (POTS) and mast cell activation syndrome (MCAS) in long COVID patients, a pattern some clinicians describe as a triad; our guide to dysautonomia symptoms covers how to recognize it.

Cognitive Testing: Documenting the Problem

If you suspect long COVID brain fog, getting formal cognitive testing serves two purposes: it validates what you’re experiencing (which matters, especially when others dismiss your symptoms), and it creates a baseline to measure improvement.

Common assessments include:

• Montreal Cognitive Assessment (MoCA): A widely used screening tool that tests attention, memory, language, and executive function. Many long COVID patients score in the mild cognitive impairment range.
• Trail Making Tests (A and B): Measure processing speed and cognitive flexibility. Long COVID patients often show slowed performance on these tests.
• Digit Span and N-back tests: Assess working memory, which is frequently impaired.
• Full neuropsychological battery: A more detailed evaluation that can pinpoint specific cognitive domains affected. This is especially useful for patients whose jobs require high cognitive performance.

Research has shown that long COVID cognitive deficits are measurable on standardized testing and are not explained by depression, anxiety, or poor effort. One UK study found cognitive deficits in long COVID patients equivalent to roughly 10 years of age-related cognitive decline.⁶

If testing confirms a deficit, that result is also useful for documentation with employers, disability insurers, or specialists. Our guide to brain fog after COVID walks through what a typical evaluation looks like and how to prepare for one.

Evidence-Based Treatments

Hyperbaric Oxygen Therapy (HBOT)

HBOT involves breathing 100% oxygen at increased atmospheric pressure, typically in a specialized chamber. The increased pressure drives significantly more oxygen into plasma, cerebrospinal fluid, and tissues than normal breathing can achieve. For a brain that’s dealing with microclot-impaired circulation and neuroinflammation, this oxygen boost can be therapeutic.

A randomized controlled trial from Tel Aviv University (the first of its kind for long COVID) showed that 40 sessions of HBOT significantly improved cognitive function, psychiatric symptoms, pain, fatigue, and sleep in long COVID patients. Brain imaging showed increased blood flow and improved microstructural integrity in brain regions associated with cognitive function.⁷

HBOT appears to work through multiple pathways: reducing neuroinflammation, promoting angiogenesis (new blood vessel growth), improving mitochondrial function, and potentially helping clear microclots. Standard protocols for long COVID typically involve 40 to 60 sessions at 1.5 to 2.0 atmospheres. You can compare providers through the national hyperbaric oxygen therapy clinic directory, and the HBOT treatment guide covers indications, contraindications, and what a session involves in more detail. Our deeper look at the HBOT long COVID clinical data breaks down the Tel Aviv trial results session by session.

NAD+ IV Infusions

Nicotinamide adenine dinucleotide (NAD+) is a coenzyme essential for mitochondrial energy production, DNA repair, and cellular signaling. NAD+ levels decline with age and are further depleted by chronic inflammation, which is exactly what’s happening in long COVID.

IV NAD+ infusions deliver the molecule directly into the bloodstream, bypassing the digestive system’s limited absorption. While large randomized trials specifically for long COVID brain fog are still underway, the biological rationale is strong. NAD+ supports mitochondrial function (critical for energy-hungry neurons), activates sirtuins (proteins involved in reducing inflammation and supporting cellular repair), and helps restore the cellular energy deficit that underlies fatigue and cognitive impairment.⁸

Clinical protocols typically involve a series of infusions over several weeks, often starting at 250 to 500 mg and titrating up. Many patients report improved mental clarity, energy, and focus after a treatment course. Clinics offering this treatment are listed in the national NAD+ IV therapy directory, and the NAD+ IV therapy guide explains dosing ranges and what an infusion appointment involves. For more on the mechanism as it relates to cognition specifically, see NAD+ for brain fog.

Low-Dose Naltrexone (LDN)

Naltrexone at standard doses (50 mg) is an opioid antagonist used for addiction treatment. At low doses (1 to 4.5 mg), it does something very different: it modulates the immune system by temporarily blocking opioid receptors on microglia and immune cells, triggering an upregulation of endorphins and a shift toward anti-inflammatory immune signaling.

LDN has been used for years in conditions involving neuroinflammation (fibromyalgia, multiple sclerosis, chronic fatigue syndrome) and is gaining traction in long COVID treatment. A retrospective study published in 2022 showed that LDN improved fatigue, pain, and cognitive symptoms in long COVID patients.⁹ It’s inexpensive, generally well-tolerated, and available through compounding pharmacies with a prescription.

Most practitioners start at 0.5 to 1 mg at bedtime and gradually increase to 4.5 mg over several weeks. Vivid dreams and mild sleep disruption are common initially but usually resolve. Our LDN guide covers the titration schedule and what to expect week by week in more detail.

Stellate Ganglion Block (SGB)

The stellate ganglion is a cluster of sympathetic nerves in the neck. A stellate ganglion block involves injecting local anesthetic (typically bupivacaine) into this nerve cluster under ultrasound guidance. It’s a procedure that has been used for decades for PTSD and complex regional pain syndrome.

The theory for long COVID: if the autonomic nervous system is stuck in a sympathetic (“fight or flight”) overdrive state, resetting it via SGB may reduce neuroinflammation and improve cerebral blood flow. Early clinical reports and small case series have shown improvements in brain fog, fatigue, and autonomic symptoms after SGB, though controlled trials are still needed.¹⁰

How Do These Long COVID Brain Fog Treatments Compare?

Each of these treatments targets a different piece of the biology described above, and none of them stands alone as a full solution. HBOT addresses oxygen delivery and neuroinflammation directly, NAD+ IV infusions target cellular energy production, LDN shifts immune signaling toward an anti-inflammatory state, and SGB addresses autonomic dysregulation. The table below summarizes what the evidence described above supports for each option.

None of these treatments works for every patient, and most are cash pay with costs that vary by clinic and region. The strongest current evidence belongs to HBOT, which is the only one of the four tested in a published randomized controlled trial for long COVID specifically. That does not mean the others lack value, it means the research base behind them is at an earlier stage.

Lifestyle Interventions That Make a Difference

Sleep Optimization

This cannot be overstated. Sleep is when the brain’s glymphatic system clears metabolic waste, including the inflammatory debris that accumulates during the day. Long COVID patients with disrupted sleep are fighting an uphill battle against neuroinflammation.

Practical steps:

• Keep a consistent sleep and wake time, even on weekends.
• Limit screen exposure for 60 to 90 minutes before bed.
• Keep the bedroom cool (65 to 68 degrees Fahrenheit).
• Address sleep apnea if present (it worsens brain fog significantly); the national sleep apnea treatment directory and sleep apnea treatment guide are useful starting points if you haven’t been evaluated.
• Consider magnesium glycinate (200 to 400 mg) before bed for sleep quality.

Exercise Pacing

Exercise is tricky with long COVID. Physical activity is generally neuroprotective and anti-inflammatory, but many long COVID patients experience post-exertional malaise (PEM), where overexertion triggers a crash in symptoms lasting days. Pushing through PEM makes things worse, not better.

The approach that works best:

• Start well below your perceived capacity.
• Use heart rate monitoring to stay in a safe zone (often 60 to 70% of max heart rate).
• Increase activity gradually, no more than 10% per week.
• Prioritize walking, gentle yoga, and light resistance training over high-intensity exercise.
• If a session triggers PEM, scale back and rest. This is information, not failure.

Because post-exertional malaise is so closely tied to the fatigue many long COVID patients experience, understanding pacing in more depth can help prevent crashes before they start; see our guide to long COVID fatigue for a fuller pacing framework.

Cognitive Rehabilitation

Just as physical therapy helps rebuild physical function, cognitive rehabilitation helps rebuild cognitive function. Working with a neuropsychologist or speech-language pathologist who specializes in cognitive rehab can be valuable.

Strategies include:

• Spaced retrieval practice: Actively recalling information at increasing intervals to strengthen memory pathways.
• External compensatory strategies: Using calendars, alarms, lists, and voice memos to reduce cognitive load.
• Attention training: Structured exercises that progressively challenge sustained attention, selective attention, and divided attention.
• Pacing cognitive activity: Breaking demanding tasks into shorter blocks with rest periods. Many patients find that 25 minutes of focused work followed by a 10-minute break (a modified Pomodoro approach) prevents cognitive crashes.

Supplements With Evidence

The supplement space is crowded and confusing. Here are the ones with the strongest biological rationale and some supporting evidence for brain fog and neuroinflammation. Our brain fog supplements guide goes into more depth on dosing and combinations if you want to go further.

Omega-3 Fatty Acids (EPA/DHA)

Omega-3s are the most well-studied anti-inflammatory supplement for brain health. DHA is a structural component of neuronal membranes, and EPA has potent anti-inflammatory effects. In the context of long COVID’s neuroinflammatory state, high-dose omega-3 supplementation (2 to 4 grams of combined EPA/DHA daily) supports the resolution of inflammation and may improve neuronal membrane fluidity. Look for a high-quality, third-party tested fish oil or algae-based supplement.

Lion’s Mane Mushroom (Hericium erinaceus)

Lion’s mane contains compounds called hericenones and erinacines that stimulate nerve growth factor (NGF) production. NGF supports the growth, maintenance, and survival of neurons. A double-blind, placebo-controlled trial in older adults with mild cognitive impairment showed significant improvement in cognitive function scores with lion’s mane supplementation.⁸ Typical dosing is 500 to 1,000 mg of extract twice daily.

Creatine

Most people associate creatine with muscles, but the brain is also a major consumer of creatine for cellular energy. Creatine supplementation (3 to 5 grams daily) has been shown to improve cognitive performance under conditions of sleep deprivation, mental fatigue, and metabolic stress, conditions that overlap substantially with the long COVID brain fog experience. It’s inexpensive, well-studied, and safe for long-term use.

Other Supplements Worth Discussing With Your Provider

• Magnesium (glycinate or threonate): Supports GABA signaling, sleep quality, and neuronal function. Magnesium threonate specifically crosses the blood-brain barrier.
• CoQ10 (ubiquinol form): Supports mitochondrial electron transport chain function. Dose: 200 to 400 mg daily.
• Curcumin (with a bioavailability enhancer like piperine or liposomal delivery): Anti-inflammatory and neuroprotective. May help reduce microglial activation.
• B vitamins (particularly B12 and folate): Essential for methylation, neurotransmitter synthesis, and myelin maintenance. Deficiency worsens cognitive symptoms.

What to Avoid

Some common approaches can actually make brain fog worse:

• Pushing through fatigue: The “just power through it” mentality triggers post-exertional malaise and can set recovery back weeks.
• Excessive caffeine: One or two cups of coffee may help, but high caffeine intake depletes already-strained adrenal reserves and worsens sleep quality. If you need caffeine to function, that’s a sign your recovery strategy needs adjustment, not more stimulants.
• Alcohol: Even moderate alcohol consumption is neurotoxic and pro-inflammatory. During active recovery from long COVID brain fog, minimizing or eliminating alcohol gives your brain the best chance to heal.
• Information overload: Spending hours researching your condition online is cognitively taxing. Set limits on research time and focus on implementing one or two changes at a time.
• Unproven “detox” protocols: Some practitioners push aggressive detox regimens that can worsen symptoms. Be cautious with anything that promises rapid results through extreme measures.

Who Treats Long COVID Brain Fog?

No single specialty owns long COVID brain fog, which is part of why patients often bounce between providers before finding one who takes a comprehensive approach. Long COVID clinics based at academic medical centers typically coordinate multiple specialists under one roof. Neurologists with a focus on neuroimmunology evaluate the inflammatory and autoimmune mechanisms described above. Neuropsychologists perform the formal cognitive testing covered earlier and design rehabilitation plans. Functional medicine practitioners and physiatrists experienced with post-infectious illness often oversee treatments like NAD+ infusions, LDN, and HBOT, and physical or occupational therapists trained in post-exertional malaise pacing help patients rebuild activity tolerance without triggering crashes.

When you’re looking for a provider, our long COVID treatment guide explains what each specialty typically offers, and the HBOT clinic directory and NAD+ IV therapy directory let you compare clinics by location and the credentials their teams hold. Being listed in a directory is not an endorsement of outcomes, so it’s still worth asking any clinic directly about its specific experience with long COVID patients.

Prognosis: Will This Get Better?

This is the question everyone asks, and the honest answer is: usually, yes, but the timeline is highly variable.

How Long Does Long COVID Brain Fog Typically Last?

Most studies show that cognitive symptoms improve over 6 to 18 months for the majority of long COVID patients. Some people recover fully within a few months. Others are still dealing with symptoms two or three years later, though usually at reduced severity.

What Predicts a Faster Recovery?

Factors that seem to predict better outcomes:

• Earlier intervention (not waiting a year to seek treatment).
• Good sleep quality.
• Appropriate activity pacing (avoiding boom-bust cycles).
• Lower baseline inflammatory markers.
• Active engagement with cognitive rehabilitation.

The encouraging news is that the brain has remarkable neuroplasticity. Given the right conditions (reduced inflammation, adequate oxygen and nutrients, appropriate cognitive challenge, sufficient rest), neural pathways can rebuild. Recovery may not be linear. You’ll likely have good days and setbacks. But the overall trajectory for most patients points toward improvement.

Building Your Treatment Plan

There’s no single protocol that works for everyone. The most effective approach combines strategies that address the underlying mechanisms driving your symptoms. A reasonable starting framework might look like:

1. Foundation: Optimize sleep, pacing, nutrition, and stress management.
2. Supplementation: Omega-3s, creatine, magnesium, and CoQ10 as baseline support.
3. Medical interventions: Discuss LDN, HBOT, and NAD+ infusions with a knowledgeable provider. Consider SGB if autonomic symptoms are prominent.
4. Cognitive rehabilitation: Work with a specialist to rebuild cognitive function systematically.
5. Monitor and adjust: Track symptoms weekly. What’s improving? What’s not? Adjust your approach based on data, not guesswork.

Finding a provider who understands long COVID and takes a multi-modal approach is worth the effort. Long COVID clinics at academic medical centers, functional medicine practitioners experienced with post-infectious illness, and neurologists specializing in neuroimmunology are all potential starting points.

For a broader overview of long COVID symptoms, treatment approaches, and the latest research developments, visit our Long COVID pillar page.

If you’re also navigating other long COVID symptoms alongside brain fog, our long COVID condition page places cognitive symptoms in the context of fatigue, dysautonomia, and the other systems the virus can affect.

Frequently Asked Questions About Long COVID Brain Fog

What does long COVID brain fog actually feel like?

Patients typically describe trouble finding words, slowed thinking, short-term memory lapses, difficulty concentrating on more than one thing at a time, and mental fatigue after tasks that used to feel automatic. It is distinct from ordinary forgetfulness because it is measurable on standardized cognitive tests and often comes paired with physical symptoms like fatigue or post-exertional crashes, not just a subjective sense of fuzziness.

How long does long COVID brain fog usually last?

Most people see measurable improvement within 6 to 18 months, and some recover within a few months of symptom onset. A smaller group of patients continues to experience symptoms two to three years out, usually at a lower severity than at onset. Earlier intervention, good sleep, and careful activity pacing are associated with faster improvement.

Is long COVID brain fog permanent?

For most patients, no. Studies of brain imaging and cognitive testing show that the underlying drivers, including neuroinflammation and blood-brain barrier leakage, can resolve as the body recovers, and the brain’s neuroplasticity allows affected pathways to rebuild over time. Recovery is rarely linear, with good days and setbacks along the way, but the overall trajectory for most people points toward improvement rather than permanent decline.

What is the most promising treatment for long COVID brain fog right now?

Hyperbaric oxygen therapy currently has the strongest clinical trial evidence, with a randomized controlled trial from Tel Aviv University showing improved cognitive function and brain imaging markers after 40 sessions.⁷ NAD+ IV infusions, low-dose naltrexone, and stellate ganglion block all have biological rationale and early supporting data, but none has been tested in a large randomized trial for brain fog specifically yet.

Can a doctor confirm long COVID brain fog with testing, or is it subjective?

It can be confirmed. Tools like the Montreal Cognitive Assessment, Trail Making Tests, and digit span testing document measurable deficits in attention, processing speed, and working memory. Research has shown these deficits are not explained by depression, anxiety, or poor effort, and one UK study found deficits equivalent to roughly 10 years of age-related cognitive decline in some long COVID patients.⁶

Does long COVID brain fog show up on an MRI or brain scan?

Standard clinical MRI often looks normal, which is part of why patients get dismissed. Research-grade imaging tells a different story: PET imaging has documented neuroinflammation in attention and memory-related brain regions,² and advanced MRI techniques have shown blood-brain barrier leakage in patients with cognitive symptoms.⁴ These findings are not yet part of routine clinical diagnosis, but they confirm the symptoms have a measurable biological basis.

Sources

1. Davis HE, McCorkell L, Vogel JM, Topol EJ. Long COVID: major findings, mechanisms and recommendations. Nat Rev Microbiol. 2023;21(3):133-146. doi:10.1038/s41579-022-00846-2 ↩
2. Braga J, Lepra M, Kish SJ, et al. Neuroinflammation after COVID-19 with persistent depressive and cognitive symptoms. JAMA Psychiatry. 2023;80(8):787-795. doi:10.1001/jamapsychiatry.2023.1321 ↩
3. Pretorius E, Vlok M, Venter C, et al. Persistent clotting protein pathology in Long COVID/Post-Acute Sequelae of COVID-19 (PASC) is accompanied by increased levels of antiplasmin. Cardiovasc Diabetol. 2021;20(1):172. doi:10.1186/s12933-021-01359-7 ↩
4. Greene C, Connolly R, Brennan D, et al. Blood-brain barrier disruption and sustained systemic inflammation in individuals with long COVID-associated cognitive impairment. Nat Neurosci. 2024;27(3):421-432. doi:10.1038/s41593-024-01576-9 ↩
5. Swank Z, Senussi Y, Manickas-Hill Z, et al. Persistent circulating severe acute respiratory syndrome coronavirus 2 spike is associated with post-acute coronavirus disease 2019 sequelae. Clin Infect Dis. 2023;76(3):e487-e490. doi:10.1093/cid/ciac722 ↩
6. Hampshire A, Trender W, Chamberlain SR, et al. Cognitive deficits in people who have recovered from COVID-19. EClinicalMedicine. 2021;39:101044. doi:10.1016/j.eclinm.2021.101044 ↩
7. Zilberman-Itskovich S, Catalogna M, Sasson E, et al. Hyperbaric oxygen therapy improves neurocognitive functions and symptoms of post-COVID condition: randomized controlled trial. Sci Rep. 2022;12(1):11252. doi:10.1038/s41598-022-15565-0 ↩
8. Mori K, Inatomi S, Ouchi K, Azumi Y, Tuchida T. Improving effects of the mushroom Yamabushitake (Hericium erinaceus) on mild cognitive impairment: a double-blind placebo-controlled clinical trial. Phytother Res. 2009;23(3):367-372. doi:10.1002/ptr.2634 ↩
9. O’Kelly B, Vidal L, McHugh T, Hennigan K, Keane J, Monaghan A. Safety and efficacy of low dose naltrexone in a long covid cohort; an interventional pre-post study. Brain Behav Immun Health. 2022;24:100485. doi:10.1016/j.bbih.2022.100485 ↩
10. Liu LD, Duricka DL. Stellate ganglion block reduces symptoms of Long COVID: a case series. J Neuroimmunol. 2022;362:577784. doi:10.1016/j.jneuroim.2021.577784 ↩

Related Reading

• Long COVID: The Complete Guide
• IV Therapy: Benefits, Risks, and What the Science Says
• Chronic Pain Management Without Opioids
• Leaky Gut Symptoms: What Science Actually Supports
• Red Light Therapy: What the Research Shows