Have you ever walked into a room and forgotten why you’re there, struggled to find words you know you should know, or felt like your brain is running on low battery, no matter how much you rest?
That heavy, fuzzy, “offline” feeling is what many people describe as brain fog, and it’s one of the most common concerns I see in practice.
Brain fog isn’t a diagnosis, but it is a signal that something in the body is out of balance. It can show up as mental fatigue, forgetfulness, poor focus, or a sense that your mind is operating at half capacity. While the experience feels similar for most people, the underlying causes can be very different.
The key to clearing brain fog is identifying why it’s happening. Tracking patterns, timing, and accompanying symptoms can reveal important clues and make the path to clearer thinking much easier to find. The following is a simple guide to understanding the underlying causes that may be driving brain fog, presented in the order that I would typically evaluate in practice.
1. Medications and Supplements
One of the first places that I start when decoding brain fog is reviewing current medications and supplements. Certain medications and supplements can trigger fog, especially:
- Antihistamines
- Benzodiazepines
- Some antidepressants
- PPIs (due to nutrient depletion)
- Hormone therapy that is too high or low
- High progesterone doses
- Stimulant “crashes.”
If your fog began soon after starting or adjusting a medication, that timeline is a key clue.
2. Nutrient Deficiencies
Nutrient deficiencies are another frequent contributor, and typically quite simple to correct. Low levels of iron, vitamin B12, vitamin D, omega-3s, and/or magnesium can all impair energy production, nerve function, or neurotransmitter balance.
Brain fog from deficiencies often develops gradually and is accompanied by symptoms such as:
- Fatigue
- Weakness
- Mood changes
- Tingling sensations
Having blood work done by your healthcare practitioner is the easiest way to confirm if these nutrient deficiencies are contributing to or causing your brain fog.
3. Poor Sleep & Fatigue
When you aren’t sleeping deeply or long enough, your brain doesn’t get the chance to reset, repair, and clear out metabolic waste. This can leave you feeling heavy-headed, unfocused, and irritable the next day.
Sleep quality is likely at the root of your brain fog you:
- Wake up unrefreshed
- Feel better on weekends
- Rely on caffeine to function
- Notice yawning throughout the day
Night sweats, pain, stress, alcohol, and sleep apnea can all weaken sleep architecture and intensify fog. Working on sleep hygiene and considering assessment for sleep apnea are great places to start.
4. Blood Sugar & Insulin Dysregulation
Blood sugar instability is another common and often overlooked cause. When your glucose levels swing up and down, your brain gets inconsistent fuel. This can create sudden fogginess, irritability, shakiness, and difficulty concentrating, especially after high-carb meals or long periods between eating.
Insulin dysregulation or reactive hypoglycemia may be to blame if your brain fog:
- Improves immediately after eating
- Feels worse after sweets or refined carbs
- Feel “hangry”
Try to include a protein and healthy fat which each meal and snack to support balanced blood sugar throughout the day to provide your brain and body with the fuel it requires.
If this sounds like you, read our article on protein and insulin resistance for more details.
5. Stress
Chronic stress and dysregulated fluctuations of stress hormones, like cortisol, change blood flow in the brain and impact the nutrients and oxygen that can be delivered. Your prefrontal cortex may become overwhelmed, which is the area responsible for focus, planning, and decision-making. This often creates a “wired but tired” type of brain fog, where your thoughts feel scattered and it’s hard to switch between tasks.
Stress-related cortisol imbalance may be the culprit if your fog comes with:
- Overwhelm
- Tension
- Anxiety
- Reliance on stimulants to get going
- Reliance on sedatives to wind down
Taking 5 deep belly breaths can quickly shift you out of a stress cycle and is a simple first step to restoring clarity.
6. Hormones
Hormonal shifts also play a key role, especially in perimenopause, menopause, postpartum phases, PMS, and thyroid disorders.
Estrogen fluctuations can disrupt neurotransmitters associated with clarity and memory, leading to fog around ovulation or before your period, often accompanied by:
- Hot flashes
- Mood swings
- Sleep disruption
Progesterone imbalance can create a more sedating, groggy fog, especially in the luteal phase. Low thyroid (hypothyroidism) produces a slow, heavy type of brain fog that appears alongside symptoms like:
- Weight gain
- Cold intolerance
- Hair thinning
- Dry skin
- Low mood
If you notice your brain fog changes with your cycle, hormones may be at the root.
7. Inflammation & Pain
Inflammatory cytokines (the chemicals in your body that create inflammation) can directly interfere with neurotransmitters and energy production, making thinking feel like a chore. Autoimmune activity, viral infections, allergies, or chronic immune activation are all common causes of inflammation that can present with brain fog. Clues here include:
- Body aches
- Swollen lymph nodes
- Fatigue
- Elevated CRP, ESR, or antibodies.
Pain from chronic conditions can also drain your cognitive resources. When your body is working overtime to manage pain, less energy is available for clear thinking. A sedentary lifestyle adds to this because limited movement reduces oxygenation and circulation to the brain. If you notice that your fog lifts after physical activity or feels worse after long periods of sitting, movement may be the missing link.
8. Mood
Anxiety, low mood, and depression all significantly influence cognitive clarity because they change how the brain prioritizes information and how much energy is available for thinking.
Anxiety creates a distracted, scattered type of brain fog where your mind jumps quickly but struggles to land. When you’re anxious, your brain shifts into hypervigilance, which pulls resources away from focus, memory, and problem-solving.
Depression, on the other hand, tends to slow cognition. People often describe feeling “underwater,” mentally fatigued, or unable to initiate tasks. Low motivation, reduced interest, and emotional heaviness all contribute to slower processing speed.
Mood-related brain fog is also common when emotional stress builds up over time, even without a formal diagnosis.
Clues include:
- Changes in appetite or sleep
- Feelings of overwhelm
- Loss of joy
- Irritability
- Persistent worry
When mood is the driver, brain fog tends to fluctuate with emotional state and often improves with:
- Therapy
- Stress reduction
- Social connection
- Physical activity
- Addressing underlying biochemical factors like:
- Low B12
- Omega-3 deficiency
- Hormonal imbalance.
Key Takeaways
While brain fog is usually reversible, it’s important to speak with a healthcare practitioner if it’s sudden, severe, worsening, affecting daily function, or paired with neurological symptoms such as slurred speech or weakness. Lab work like CBC, ferritin, B12, thyroid panel, vitamin D, fasting glucose/insulin, and inflammatory markers can be extremely helpful.
Brain fog is your body’s way of telling you something is off. When you understand the pattern and context of your symptoms, the cause becomes easier to pinpoint and the path to clearer thinking becomes much more accessible.
