Busting Myths About Cloudy Thinking: What Are The Real Causes of Brain Fog?

Brain fog, a term used for sluggish thinking, forgetfulness, and lack of focus, affects people for countless reasons. However, brain fog is rarely talked about in your doctor's office-- with the attention on memory loss instead. What's more, information you find online can often be incomplete at best and flat-out wrong at worst. But we've got good news, while the triggers behind brain fog can be complicated, the solutions are easier than you might think.

Key Takeaways

• Brain fog is frequently linked to inflammation caused by conditions like autoimmune diseases, chronic fatigue syndrome, and obesity.

• Fluctuations in hormones during pregnancy, menopause, or due to conditions like hypothyroidism or low testosterone can impair cognitive function.

• Better sleep, exercise, stress relief, and a nutrient-rich diet are effective ways to reduce brain fog and enhance mental clarity.

What is Brain Fog?

You won’t find brain fog listed in a medical dictionary because it’s not a medical condition as such. Rather, the phrase describes a constellation of symptoms that give rise to sluggish cognition.

The history of brain fog goes back almost two centuries, when it was used to describe the mental exhaustion experienced by “brainworkers” like lawyers and teachers. But the phrase only came into its own in the 1990s when it was linked with chronic fatigue syndrome (CFS), also known as Myalgic Encephalomyelitis (ME), and autoimmune disorders that were being highlighted at that time.

Since then, scientists have been asking, "What causes fogginess?" and they've uncovered more questions than answers. For one thing, they've learned that brain fog is caused by a lot more than autoimmune illnesses. From poor sleep and anxiety to viral infections like COVID-19 and chemo-brain, brain fog can result from numerous physical and mental challenges.

It’s not always easy for patients to describe their cognitive fog; they know their brains aren’t working as they should be. Interestingly, and what’s baffling, is that they may still perform well on cognitive tests, not appearing to have any cognitive impairment at all! ¹

Brain fog symptoms patients describe include:

• Inability to focus, concentrate, or pay attention

• Forgetfulness

• Confusion or feeling spaced out

• Difficulty processing information

• Hard to multitask

• Mental sluggishness or exhaustion

• Losing train of thought

• Unable to find the right words

People can suffer from a foggy brain for multiple reasons. Finding the root cause can require detective work worthy of Sherlock Holmes, as there are plenty of places to look, including lifestyle, diet, nutritional deficiencies, hormonal factors, medical conditions, and medications.

Let’s start with...

Brain Fog Cause: Medical Conditions Stoking Inflammation

Many common medical conditions can significantly impact cognitive function by disrupting normal brain chemistry and inflammation levels. In fact, inflammatory molecules secreted in the brain are linked to many medical conditions and are thought to be an underlying cause of brain fog. ² These conditions include:

Migraine: Sufferers commonly report that their concentration and memory can be impacted before, during, and after a migraine attack.

Autoimmune diseases: Some autoimmune diseases, such as lupus, Crohn’s disease, celiac disease, and rheumatoid arthritis, involve inflammation throughout the body, leading to brain fog symptoms. Others, like multiple sclerosis, directly affect the brain and central nervous system by eroding the myelin sheath that surrounds nerves. This slows or stops the transmission of electrical impulses, causing a range of neurological symptoms, including brain fog.

Fibromyalgia: This condition causes pain throughout the body and affects concentration, thinking, and memory, dubbed fibro fog. Changes to signaling pathways in the brain that transmit pain impulses are believed to contribute to the patients’ fogginess.

Chronic Fatigue Syndrome (CFS)/Myalgic Encephalomyelitis(ME): Brain fog is a feature of this condition, with symptoms fluctuating from mild to severe. Cognitive and physical fatigue lasts at least six months and can continue for years.

Inflammatory Infections: If the brain becomes a target for infections, it can lead to cognitive problems. These include Lyme disease, exposure to mold, West Nile virus, and COVID-19. Infections like these are one reason for brain fog.

Almost one in five people who have COVID-19 don’t shake it off within a few weeks and develop Long COVID-19. In these patients, certain types of immune cells are thought to be activated in the brain. This leads patients to commonly complain of “muddled or fuzzy thoughts.” Research shows that conditions like long COVID-19 can reduce brain processing speed by up to 30%.

Mood disorders: Raised levels of inflammatory markers in the brain are found in people diagnosed with anxiety, and there’s evidence that some people with depression also have brain inflammation. This may be why these disorders can affect people’s ability to think and remember.

Obesity: This can lead to inflammation all over the body, including the brain, which may be why obese people often report brain fog.

Seasonal Allergies: Many experience brain fog during the allergy season. The body responds to those affected by producing histamines and proteins called cytokines, resulting in inflammation.

Hormonal Factors Leading to Brain Fog

Brain functioning can be affected by changes – either up or down - in hormone levels. During pregnancy, estrogen and progesterone are elevated and this can affect cognition. Four out of five pregnant women report “baby brain” with forgetfulness being the most reported problem among many others including poor attention and concentration.

At menopause, it’s a repeat performance except this time estrogen levels drop, giving rise to poor concentration, memory problems, and woolly thinking. In fact, hormonal changes during menopause can temporarily decrease memory function by 15-20%.

Men don’t escape either, as low testosterone levels can cause difficulties in thinking clearly.

One common medical condition that can cause brain fog is hypothyroidism. A drop in thyroid hormone can lead to increased forgetfulness, difficulty finding the right word, and slow thinking. These problems are not always resolved with thyroid medication. ³

Brain Fog In Your Medicine Cabinet

The fuzzy thinking and mental cloudiness you're experiencing might be coming from an unexpected source—your medicine cabinet. Both prescription and over-the-counter medications can significantly impair cognitive function by disrupting the delicate balance of hormones and neurotransmitters that keep your brain sharp and focused. 4

Sleep medications rank among the most common culprits behind medication-induced brain fog. A 2018 study published in the Journal of Clinical Sleep Medicine found that 59% of people taking prescription sleep aids reported morning grogginess and difficulty concentrating, with effects sometimes lasting well into the afternoon. Even more concerning, research from the British Medical Journal suggests regular users of sleeping pills have a 30% higher risk of developing long-term memory problems.

Pain medications, particularly opioids, can leave you feeling mentally sluggish while providing relief for physical discomfort. According to a University of California study, approximately 42% of long-term opioid users report significant cognitive side effects. Even common over-the-counter options aren't immune—a 2016 study found that regular users of specific NSAIDs experienced a 10 to 15% reduction in information processing speed.

Migraine and seizure medications often come with cognitive trade-offs. A comprehensive review in Neurology found that up to 38% of patients taking anti-epileptic drugs experience some form of memory impairment, with verbal recall being particularly affected. When these same medications are used for migraine prevention, approximately one in four patients reports difficulties with word-finding and mental clarity.

Arthritis treatments involving corticosteroids can take a cognitive toll when used long-term. Research published in the Journal of Rheumatology showed that patients on prednisone for more than six months experienced twice the rate of concentration problems compared to those using non-steroid alternatives. The effect appears dose-dependent, with higher doses leading to more pronounced cognitive symptoms.

Psychiatric medications for anxiety and depression sometimes create the very mental fog they're meant to help clear. A surprising finding from a large-scale European study revealed that approximately 35% of patients taking certain SSRIs and 42% of those on benzodiazepines reported some degree of cognitive dulling or emotional blunting—a frustrating side effect when mental clarity is already compromised.

Allergy medications, particularly first-generation antihistamines, are notorious cognitive disruptors. A NASA study found that diphenhydramine (found in many allergy and sleep aids) impaired cognitive performance more than alcohol at the legal driving limit. Nearly 73% of regular users reported noticeable difficulties with focus and mental acuity, yet many don't connect these symptoms to their allergy relief.

Chemotherapy's impact on cognition has become so widely recognized that researchers gave it a specific name: "chemo brain." According to the American Cancer Society, up to 75% of cancer patients receiving chemotherapy experience cognitive changes during treatment, with approximately 35% reporting persistent effects for months or years afterward. Patients describe a constellation of symptoms—from inability to multitask to forgetting familiar words—that significantly impact quality of life even as they recover physically.

If you notice brain fog symptoms not long after taking a new medication, this would be a good clue that the drug is to blame. A change in dosage or a different drug may resolve cognitive issues.

Lifestyle Factors Reaping Brain Havoc

Poor sleep

Sleep isn't just a daily timeout – it's your brain's essential maintenance period. During deep sleep, your brain flushes out toxic proteins that build up during waking hours, similar to a nighttime cleaning crew. Research from the National Institutes of Health shows that this "glymphatic system" is up to 10 times more active when sleeping, making those seven to nine hours crucial for keeping our mental machinery running smoothly.

The statistics paint a concerning picture of our collective sleep deficit. While seven to nine hours is the sweet spot for optimal brain function, a startling 2022 American Academy of Sleep Medicine survey found that 32% of working adults get by on six or fewer hours of sleep. Even more troubling, chronic sleep deprivation has been linked to a 30% reduction in working memory capacity and a 40% decrease in our ability to form new memories.

This helps explain why a poor night's sleep can leave you fumbling for words or struggling to remember where you put your keys. No wonder so many people complain of fuzzy thinking, poor concentration and confusion.

Not enough exercise (Prolonged sedentary time)

When we sit for extended periods, we're not just affecting our bodies – we're starving our brains of vital resources. Research from the University of California shows that physical inactivity reduces blood flow to the brain by up to 20-30%, particularly in regions crucial for memory and problem-solving. This decreased circulation means less oxygen and fewer nutrients reaching our brain cells, creating the perfect storm for mental fog and sluggish thinking.

Chronic stress

Stress reduces blood flow to the brain, impacting memory, and leads to mental exhaustion, making it difficult to think clearly.

Nutritional deficiencies and trigger foods

If your brain isn’t provided with the raw materials it needs to function, you can suffer from brain fog.

Ultraprocessed foods, high in unhealthy fats and sugars and low in essential nutrients, lead to brain inflammation and thinking that's not as clear as it should be. Dehydration also impacts the ability to think, as can drinking too much alcohol and caffeinated drinks. People with food allergies or sensitivities can also develop brain fog if they eat an offending food.

Resolving Brain Fog

Not all cases of brain fog can be resolved easily if they are a feature of an incurable medical condition, or a medication side effect, but for anything else, there are strategies to clear away the mental fog. ⁵

As we talked about before, if brain fog develops after a new medication, then please speak to your doctor or pharmacist about a change of dose or an alternative medication. Or avoid medication altogether. For instance, instead of antihistamines for seasonal allergies, try natural options like saline rinsing and nasal balms.

Get a good night’s sleep

The impact of sleep deprivation goes beyond just feeling tired. When we consistently shortchange our sleep, we're changing how our brain functions on a cellular level. Studies show that just one night of poor sleep can increase inflammation markers in the brain by up to 20%, disrupting the neural networks responsible for focus, decision-making, and emotional regulation. This explains why sleep-deprived individuals often report feeling like they're thinking through mud – their brain's processing speed quite literally slows down, making every mental task require more effort than usual. Aim for at least seven hours of sleep, keep a regular sleep schedule, and set up your sleep environment to optimize your chances of sleeping well. This involves keeping the bedroom quiet, dark, and cool, keeping electronic devices out of the bedroom, putting any devices away an hour before bedtime, and not eating for at least three hours before retiring.

If you suffer from sleep disorders such as sleep apnea, disrupted sleep can affect cognitive function and have serious consequences for your whole body, so it's a good idea to seek medical help.

Get moving

Prolonged sitting is harmful to the brain and overall health even, surprisingly, for those who go the gym each day.

The impact of a sedentary lifestyle on cognitive function is striking. A landmark 2021 study in the Journal of Applied Physiology found that adults who sat for more than 8 hours daily showed a 15% decrease in cognitive performance compared to their more active peers. Even more concerning, researchers at UCLA discovered that sedentary individuals had up to 10% less brain volume in regions associated with memory and attention, suggesting that too much sitting might shrink key areas of our brain over time.

As Italian scientists write: physical exercise “induces structural and functional changes in the brain, determining enormous biological, and psychological benefits.” ⁶

So get moving any way you can. Even a simple activity like walking can greatly affect how you feel. Breaking up periods of inactivity with movement can have immediate benefits. Studies show that just five minutes of walking every hour can increase brain blood flow by up to 15%, while regular exercise boosts levels of BDNF (Brain-Derived Neurotrophic Factor) – often called "Miracle-Gro for the brain" – by up to 300%. This crucial protein helps create new neural connections and protect existing brain cells, acting as a natural brain fog fighter. The evidence is clear: our brains work better when our bodies move regularly.

Stimulate your brain

Recent research in neuroscience has revealed just how powerful mental challenges can be for brain health. A groundbreaking 2019 study in the International Journal of Geriatric Psychiatry found that adults who regularly engaged in puzzles and board games had cognitive function equivalent to someone 10 years younger, particularly in memory and reasoning tasks. Even more impressive, researchers at the University of Exeter discovered that people who played games like chess or completed crosswords daily showed a 74% reduction in cognitive decline compared to those who rarely exercised their minds with such activities.

The benefits of mental stimulation extend beyond just maintaining cognitive function – they actively enhance it. A study published in the Journal of Neuroscience showed that participants who spent just 15 minutes daily on challenging brain games improved their processing speed by 33% over six weeks. The brain's remarkable plasticity means it responds quickly to mental exercise: participants in a Memory Challenge Study at Harvard Medical School demonstrated a 40% improvement in attention span and a 59% boost in problem-solving abilities after completing daily cognitive training exercises for one month. Think of your brain like a muscle – each puzzle, game, or new learning experience acts like a mental workout, strengthening neural connections and building cognitive reserve.

Chill out

When life is hectic it’s difficult to make time for yourself, but your brain needs a break. Find time for activities you enjoy, meet up with friends, take a daily walk, read a novel, learn meditation or deep breathing techniques.

Deep relaxation techniques like meditation and mindful breathing trigger your body's parasympathetic nervous system, reducing stress hormones like cortisol by up to 50% while increasing blood flow to your brain. This physiological shift helps clear mental cloudiness by allowing your brain to shift from "fight or flight" mode to "rest and digest," where it can process information more efficiently and restore mental clarity.

If needed, explore cognitive behavioral therapy.

Eat more nutritious food

A natural, healthy, nutrient-dense diet is good for the brain and the whole body.

One such diet was developed to support brain health specifically. It’s called the MIND diet. Berries and green leafy vegetables take center stage together with whole grains, other veg, beans, nuts, poultry, fish, olive oil, and wine in moderation.

This diet also counters inflammation. In addition, drink adequate amounts of water and don’t go over the top on alcohol and caffeine.

Support your brain with nutritional supplements

Many essential nutrients play key roles in the brain but are commonly deficient in the diet. Magnesium is needed for healthy psychological and cognitive performance, and its deficiency can lead to brain fog.

Yet as a Harvard scientist writes: “its consumption has significantly decreased in the last few decades because of changes in dietary habits; furthermore, removal of magnesium during food processing also contributes to reduced magnesium uptake.” ⁷

The same story can be told for many other essential nutrients like omega-3s (which can improve cognitive function by up to 26%), vitamin B12 (critical for neural function), and adaptogens like Lion's Mane mushroom (shown to reduce mild cognitive impairment by 30% in clinical trials) can help combat mental cloudiness.

Additionally, natural nootropics like Bacopa monnieri and ginkgo biloba have been clinically proven to enhance memory and mental processing speed, with research showing improvements in cognitive performance of 23% and 38%, respectively, in controlled studies.

So it’s important to plug nutritional gaps and provide additional nutritional support to clear foggy thinking.

Summary

Brain fog describes a sense of mental cloudiness, forgetfulness, and difficulty concentrating. Often linked to inflammation, hormonal changes, medications, or lifestyle factors like poor diet and stress, brain fog can sometimes stem from underlying medical conditions. While resolving brain fog may require medical advice in chronic cases, most people can experience improvement by adopting lifestyle changes such as better sleep, a nutrient-dense diet, regular exercise, and stress management.

Frequently Asked Questions

What is the root cause of brain fog?

It doesn’t have a single root cause as such. It can come about for many reasons, ranging from a lack of sleep to a serious medical condition that affects the brain.

What deficiency causes brain fog?

It may or may not be caused by a deficiency. But many nutrients are directly involved with brain health. These include the vitamin B complex, especially B12, vitamin C, and vitamin D, and the minerals magnesium and zinc among others.

How do you clear up brain fog?

By working through various strategies. These can range from changing a drug prescription or getting a full night’s sleep to taking up exercise, relieving stress, revamping the diet, or taking a brain-supporting supplement.

Can brain fog be permanent?

How long it lasts will depend on the underlying cause. For instance, it should resolve after pregnancy, menopause or Long COVID, but may persist with chronic fatigue/ME, and autoimmune diseases. Successful disease management and addressing diet and lifestyle factors will help in most cases.

What foods help clear brain fog?

Foods rich in antioxidants, healthy fats, vitamins, and minerals—like leafy greens, berries, fish, nuts, and seeds—can support brain health and reduce fog.