A patient walked into my office last month with a story I hear often. She'd seen three doctors, undergone extensive testing, and heard the same refrain each time: Everything looks normal. Yet she couldn't focus at work, forgot simple tasks, and felt like she was thinking through fog.

The problem wasn't that her test results were normal; it was that no one had ordered the right tests. They were looking for disease when they should have been looking for dysfunction.

Brain fog isn't "in your head”; it's a real symptom with identifiable physiological causes. More importantly, it's your brain's way of telling you something specific is wrong. The key is understanding what.

By the end of this article, you'll understand the seven most common root causes of brain fog, how to identify which one (or ones) applies to you, and what to do about it. Let's start with what we know from both clinical research and thousands of patient experiences.

The Seven Most Common Causes of Brain Fog

After treating hundreds of patients with cognitive symptoms over the years at a renowned medical facility, I've identified seven primary causes that account for the vast majority of brain fog cases. Understanding these patterns is the first step toward clarity.

1. Hormonal Changes

Hormones are powerful modulators of brain function, and even subtle shifts can have dramatic cognitive effects. This is perhaps the most under-recognized cause of brain fog in conventional medicine.

One of our patients—my wife Pepie, an occupational therapist who dedicates her career to restoring function to people's lives—experienced this firsthand during fertility treatment. The dramatic hormone fluctuations from IVF medication created brain fog so severe it affected her ability to do the detailed clinical work she loved. What struck us both was how invisible this side effect was—her fertility doctor focused entirely on reproductive outcomes, while the cognitive impact went unaddressed.

Common hormonal triggers include:

•        Perimenopause and menopause (estrogen and progesterone fluctuations)

•        Pregnancy and postpartum (dramatic hormone shifts)

•        Thyroid disorders (even subclinical hypothyroidism)

•        Fertility treatments (IVF medications create rapid, significant hormone changes)

•        Hormonal birth control (synthetic hormones affect some women's cognition)

The mechanism: Estrogen affects neurotransmitter production, cerebral blood flow, and neuroplasticity. When levels fluctuate or decline, cognitive function can follow. Many women describe it as "feeling like myself one day and unable to think the next."

2. Sleep Deprivation and Sleep Disorders

Sleep isn't just rest—it's when your brain performs essential maintenance. During deep sleep, your brain clears metabolic waste products (including beta-amyloid, associated with Alzheimer's disease) through the glymphatic system. Without adequate quality sleep, these toxins accumulate, leading to impaired cognition.

But here's what most people miss: quality matters more than quantity. You can spend eight hours in bed but wake up foggy if you're not reaching deep, restorative sleep stages.

Red flags for sleep-related brain fog:

•        Waking unrefreshed despite adequate time in bed

•        Snoring, gasping, or witnessed breathing pauses (sleep apnea)

•        Excessive daytime sleepiness

•        Brain fog that improves on vacation (when you finally catch up on sleep)

•        Morning headaches (another potential sign of sleep apnea)

Sleep apnea, in particular, is dramatically underdiagnosed and can cause severe cognitive impairment. If you snore loudly or your partner notices breathing pauses, pursuing a sleep study could be life-changing.

3. Chronic Stress and Burnout

Chronic stress doesn't just make you feel overwhelmed—it physically changes your brain. Elevated cortisol (your primary stress hormone) over extended periods impairs the hippocampus (memory center) and prefrontal cortex (executive function). This is why burnout isn't just "being tired"—it's a state of cognitive and physiological dysfunction.

In my neurology practice, I see this constantly in high-performing professionals who've pushed through stress for years. Their bodies finally say "enough" through symptoms like brain fog, difficulty concentrating, and memory problems.

Signs your brain fog stems from chronic stress:

•        Worse during or after stressful periods

•        Accompanied by anxiety, irritability, or emotional exhaustion

•        Difficulty "turning off" your mind

•        Physical tension (tight shoulders, jaw clenching)

•        Feeling overwhelmed by previously manageable tasks

The good news: Unlike some causes, stress-related brain fog often responds well to targeted intervention. The bad news: It requires actually addressing the stress, not just supplementing around it.

4. Nutritional Deficiencies

Your brain is metabolically demanding, consuming about 20% of your body's energy despite being only 2% of your body weight. When specific nutrients are insufficient, cognitive function suffers—often before you develop other obvious symptoms.

The most common deficiencies I see contributing to brain fog:

•        Vitamin B12 (especially in vegetarians, vegans, or those over 50)

•        Vitamin D (affects neurotransmitter synthesis)

•        Iron (particularly in menstruating women—ferritin should be >50 ng/mL)

•        Magnesium (involved in over 300 enzymatic reactions, many affecting brain function)

•        Omega-3 fatty acids (essential for brain cell membrane integrity)

Here's the frustrating part: Standard lab ranges for these nutrients are often too broad. You can be "normal" on paper while being functionally deficient. This is why I often recommend optimal ranges rather than just ruling out severe deficiency.

5. Medications and Medical Treatments

Many medications can cause cognitive side effects, even when they're necessary and beneficial for their primary purpose. The challenge is that these effects often develop gradually, making the connection less obvious.

Common cognitive culprits:

•        Antihistamines (especially older "drowsy" versions, but even newer ones affect some people)

•        Benzodiazepines and sleep medications

•        Some blood pressure medications (particularly beta-blockers)

•        Statins (in a subset of users)

•        Certain antidepressants

•        Fertility treatments (the hormone medications, not the procedures themselves)

In Pepie's case with IVF, the dramatic estrogen surges and fluctuations from medication created brain fog that interfered with her work as an occupational therapist—precisely when she needed to be at her sharpest to help her patients restore function to their lives. This experience of cognitive impairment during an already challenging time ultimately inspired us to create Iatrogenix, with a mission to help people restore themselves back to their optimal selves, even when medical treatments create temporary setbacks.

Important: Never discontinue prescribed medications without consulting your doctor. But do have an honest conversation about whether cognitive side effects might be medication-related.

6. Inflammation and Autoimmune Conditions

Chronic inflammation—whether from autoimmune disease, chronic infection, or inflammatory conditions—can significantly impact brain function. The mechanism involves inflammatory cytokines crossing the blood-brain barrier and affecting neurotransmitter metabolism.

Post-COVID brain fog has brought massive attention to this mechanism. Many people who had COVID-19, even mild cases, developed persistent cognitive symptoms that can last months or years. The inflammation triggered by the virus appears to affect brain function long after the acute infection resolves.

Other inflammatory causes include:

•        Autoimmune conditions (lupus, rheumatoid arthritis, Hashimoto's thyroiditis)

•        Chronic infections (Lyme disease, Epstein-Barr virus reactivation)

•        Inflammatory bowel disease

•        Chronic exposure to inflammatory triggers (mold, environmental toxins)

The hallmark of inflammatory brain fog is that it often comes with other symptoms: fatigue, joint pain, low-grade fevers, or general malaise. If your brain fog appeared after an illness or alongside physical symptoms, inflammation is a strong possibility.

7. Blood Sugar Dysregulation

Your brain runs primarily on glucose. When blood sugar levels fluctuate dramatically—whether too high, too low, or simply unstable—cognitive function suffers. This is one of the most overlooked causes of brain fog, particularly in people without diabetes.

You don't need to be diabetic to experience cognitive effects from blood sugar issues. Reactive hypoglycemia (blood sugar crashes after meals) and insulin resistance (where cells become less responsive to insulin) both commonly cause brain fog.

Signs your brain fog relates to blood sugar:

•        Worse when hungry or after high-carbohydrate meals

•        Improves after eating protein

•        Accompanied by energy crashes, shakiness, or irritability

•        Craving sugar or simple carbohydrates

•        Family history of diabetes or metabolic syndrome

The good news: Blood sugar-related brain fog often responds quickly to dietary changes and lifestyle modifications.

How to Identify YOUR Root Cause

Now that you understand the seven primary causes, let's determine which applies to you. Most people fall into clear patterns when they answer these questions systematically.

Use this decision tree approach:

Start with timing

When did your brain fog begin?

•        After an illness → Consider inflammation/infection (especially post-viral)

•        During perimenopause/pregnancy/IVF → Likely hormonal

•        After starting a new medication → Medication-related

•        During or after a stressful life period → Stress/burnout

•        Gradual onset over months/years → Consider nutritional, thyroid, or sleep issues

Consider patterns

When is your brain fog worse?

•        Mornings → Sleep quality issue

•        Afternoons (especially after lunch) → Blood sugar, food sensitivities

•        During certain times of menstrual cycle → Hormonal

•        After stressful days → Stress/burnout

•        Constant/no pattern → Consider nutritional deficiency, thyroid, or chronic inflammation

Look at accompanying symptoms

What else are you experiencing?

•        Fatigue, weight changes, cold intolerance → Thyroid

•        Hot flashes, irregular periods, mood swings → Perimenopause

•        Snoring, morning headaches, daytime sleepiness → Sleep apnea

•        Joint pain, rashes, fevers → Inflammation/autoimmune

•        Anxiety, racing thoughts, tension → Stress/burnout

•        Shakiness when hungry, cravings → Blood sugar

When to see a doctor versus self-manage

See a doctor if:

•        Brain fog appeared suddenly or is rapidly worsening

•        You have concerning neurological symptoms (weakness, vision changes, severe headaches)

•        You suspect hormonal, thyroid, or other medical issues requiring testing

•        You're taking medications that might be contributing

Consider self-management first if:

•        The cause seems clearly related to sleep, stress, or diet

•        You haven't yet tried basic interventions

•        The onset was gradual and symptoms are stable

What the Science Says About Brain Fog

While "brain fog" isn't a medical diagnosis, the underlying mechanisms are increasingly well understood. Let's look at the physiological basis for why these seven causes impair cognition.

Mitochondrial Dysfunction

Your brain cells require enormous amounts of energy to function. This energy comes from mitochondria—the "power plants" of your cells. When mitochondria don't work efficiently, brain cells can't maintain normal function.

Multiple brain fog causes impair mitochondrial function: nutrient deficiencies (especially B vitamins and magnesium), inflammation, chronic stress, and poor sleep all reduce mitochondrial efficiency. This helps explain why brain fog from different causes can feel similar—they converge on a common pathway of energy dysfunction.

Neuroinflammation

Inflammation in the brain—neuroinflammation—disrupts normal neuronal signaling and can damage brain tissue over time. This inflammation comes from various sources: systemic inflammatory conditions, immune activation from infections, or metabolic dysfunction.

Research on post-COVID brain fog has revealed persistent neuroinflammation months after infection. This same mechanism likely explains brain fog from other inflammatory triggers. The inflammatory cytokines that circulate during chronic inflammation can cross the blood-brain barrier and directly impair cognitive function.

Blood-Brain Barrier Integrity

The blood-brain barrier is a selective filter that protects your brain from harmful substances while allowing necessary nutrients through. When this barrier becomes "leaky," substances that should stay out of the brain can enter, triggering inflammation and dysfunction.

Chronic stress, poor sleep, and inflammation can all compromise blood-brain barrier integrity. This creates a vicious cycle: barrier breakdown allows more inflammatory triggers into the brain, which further damages the barrier.

Neurotransmitter Imbalance

Brain cells communicate via neurotransmitters—chemical messengers like serotonin, dopamine, and acetylcholine. Production of these neurotransmitters requires specific nutrients and is modulated by hormones.

Nutritional deficiencies (especially B vitamins, amino acids, and minerals) and hormonal changes (estrogen directly affects neurotransmitter production) both disrupt this delicate balance. Even mild imbalances can cause noticeable cognitive symptoms.

Why Brain Fog Is Often Multi-Factorial

Here's what I've learned from years of clinical practice: brain fog rarely has just one cause. More often, it's the combination of factors that pushes someone over the threshold into symptoms.

I call this the "threshold effect." Your brain can compensate for one or two stressors—maybe you're a bit sleep deprived, or your vitamin D is low, or you're experiencing some work stress. Each factor alone might not cause obvious problems. But when multiple factors combine, they exceed your brain's compensatory capacity, and symptoms emerge.

In Pepie's case, it was a perfect storm: the dramatic hormonal fluctuations from IVF medications, the emotional stress of fertility treatment, and the sleep disruption from both the medication side effects and the anxiety about the process. Any one of these might have been manageable. Together, they created brain fog severe enough to interfere with her ability to provide the detailed, focused care her occupational therapy patients needed.

This multi-factorial reality is why a comprehensive approach works better than targeting just one area. Improving sleep helps. Reducing stress helps. Supporting hormone balance helps. But doing all three creates synergistic improvement that exceeds what any single intervention provides.

It also explains why some people feel frustrated when addressing one factor doesn't resolve their symptoms. You might fix your vitamin D deficiency but still have brain fog because there are two other contributing factors still present. This isn't failure—it's information. It tells you to look at the other pieces of the puzzle.

First Steps for Each Cause Type

Based on what you've identified as your likely cause(s), here are immediate action steps you can take:

For Hormonal Brain Fog

•        Track symptoms against your menstrual cycle to identify patterns

•        Get comprehensive thyroid testing (TSH, Free T4, Free T3, Reverse T3, antibodies)

•        Consider supplements that support hormone balance (specific recommendations in premium guide)

•        For IVF/fertility treatment: Talk to your doctor about cognitive support options

For Sleep-Related Brain Fog

•        Maintain consistent sleep-wake times (yes, even on weekends)

•        Optimize your sleep environment (dark, cool, quiet)

•        If snoring or breathing pauses, talk to your doctor about a sleep study

•        Consider magnesium glycinate before bed (supports sleep quality)

For Stress and Burnout Brain Fog

•        Implement daily stress reduction (even 10 minutes of meditation helps)

•        Prioritize sleep—this is non-negotiable for stress recovery

•        Consider adaptogenic herbs (ashwagandha, rhodiola) to support stress response

•        If severe, work with a therapist—this is a medical issue, not a character weakness

For Nutritional Deficiency Brain Fog

•        Get comprehensive blood work (B12, vitamin D, ferritin, magnesium RBC)

•        Start a high-quality multivitamin while waiting for test results

•        Focus on nutrient-dense whole foods

•        Consider omega-3 supplementation (high-quality fish oil or algae oil)

For Medication-Related Brain Fog

•        Document when brain fog started relative to medication changes

•        Have an honest conversation with your prescribing doctor

•        Never stop medications without medical guidance

•        For unavoidable medications, ask about cognitive support strategies

For Inflammatory Brain Fog

•        Get inflammatory markers tested (high-sensitivity CRP, ESR)

•        Focus on anti-inflammatory diet (Mediterranean-style eating)

•        Consider omega-3s and curcumin supplementation

•        For post-viral symptoms, be patient—recovery takes time but does occur

For Blood Sugar-Related Brain Fog

•        Get fasting glucose and HbA1c tested

•        Balance meals with protein, healthy fats, and fiber

•        Avoid eating carbohydrates alone (always pair with protein/fat)

•        Consider chromium or berberine supplementation

•        Regular exercise significantly improves insulin sensitivity

Moving Forward

Brain fog is frustrating, but it's not permanent and it's not "all in your head." It's a legitimate symptom with identifiable causes—and most importantly, addressable causes.

The key is approaching it systematically: identify your most likely cause(s), address the fundamentals first (sleep, stress, nutrition), get appropriate testing, and then implement targeted interventions.

For many people, this process takes several weeks to months. That timeline can feel long when you're struggling daily, but remember: you're not just treating symptoms, you're correcting underlying dysfunction. That takes time, but the results tend to be lasting.

Our experience creating Iatrogenix came from Pepie's journey through IVF-related brain fog—and her professional perspective as an occupational therapist who helps people restore function to their lives. When she couldn't find adequate support for the cognitive effects of her fertility treatment, we realized there was a gap in how medicine addresses these "in-between" symptoms. Our mission became helping people restore themselves back to their optimal selves, especially during medical treatments or life transitions that temporarily compromise cognitive function.

Whether you address your brain fog through lifestyle changes, medical treatment, targeted supplementation, or a combination approach, the important thing is that you start. You deserve to think clearly, work effectively, and feel like yourself again. That's not just possible—it's probable with the right approach.

About the Author

Dr. Nick Tzikas, MD, MPH, is a board-certified headache medicine specialist. He serves as Assistant Professor of Neurology and Medicine at a renowned medical facility, where he directs multiple headache clinics and co-directs the Headache Medicine Fellowship program. As a nationally recognized Key Opinion Leader in migraine therapeutics, Dr. Tzikas advises pharmaceutical companies on clinical trials and drug development while maintaining an active clinical practice treating patients with complex neurological conditions.

Dr. Tzikas co-founded Iatrogenix with his wife Pepie, an occupational therapist, after witnessing the gap in cognitive support during her fertility treatment. Their mission is to provide evidence-based solutions that help people restore themselves to their optimal selves during medical treatments and life transitions. Dr. Tzikas brings academic rigor and clinical expertise to every Iatrogenix formulation, ensuring products meet the same standards he'd recommend to his own patients.

Learn more at iatrogenix.com

Medical Disclaimer

This article is for educational and informational purposes only and is not intended as medical advice. The information provided should not be used for diagnosing or treating a health problem or disease. Always consult with your healthcare provider before starting any new supplement regimen, making changes to existing medications, or if you have questions about a medical condition.

If you are experiencing severe or sudden cognitive changes, neurological symptoms, or any medical emergency, seek immediate medical attention. The suggested interventions in this article are not a substitute for professional medical care and should be implemented under appropriate medical supervision.