What Is Brain Fog? A Neurologist Explains

Brain fog is a common way to describe the feeling that your mind is working harder than it should. However, it’s not an official medical diagnosis — it’s an everyday expression that has become popular in public discourse.

“It’s not a medical term, not a diagnosis, not a cause,” says Daniel Lee, MD, a neuropsychiatrist at OhioHealth. Brain fog is when normal mental tasks require more effort. Patients often describe it this way: “I can do the task; it just takes me a lot more effort and time.”

Brain fog usually doesn’t mean you’re forgetting recent conversations or repeating yourself. It tends to affect working memory, the mental scratch pad that holds information for a few seconds, like a phone number you remember just long enough to write down.

What are the most common brain fog symptoms?

Brain fog looks different from person to person, but most people describe some combination of these experiences:

• Tasks take noticeably longer than usual.
• Thinking feels slow or sluggish.
• Focusing is difficult, and attention feels scattered.
• Holding information in your mind for a few seconds is harder than normal.
• Mental work leaves you drained.
• Your mind feels hazy, cloudy or unclear.

These symptoms are real, even when they’re hard to measure.

What causes brain fog?

Because brain fog is a symptom, not a condition, and can have many possible causes. Your lifestyle, age and other symptoms help point toward the likely source. “Brain fog kind of looks the same regardless of the underlying cause. So, it’s important to look at the accompanying symptoms and lifestyle factors to understand which diagnostic tests and therapies ought to be considered,” says Dr. Lee.

Lifestyle factors

“Sleep, mood and stress are probably the biggest culprits,” Dr. Lee says. For younger adults, especially, lifestyle factors like these are typically the most common causes. They are also the most modifiable causes, meaning that it’s much easier to change your day-to-day routine to ease the brain fog you might be feeling,

• Sleep: Lack of sleep or an interrupted sleep routine is the most common cause of brain fog, and it doesn’t take much sleep deprivation to cause it.
• Stress and anxiety: When a lot is on your mind, attention can become fragmented. The link between brain fog and anxiety is strong, especially with clinical depression or anxiety.
• Substances: Alcohol, cannabis and other substance use can contribute to brain fog.

Hormonal factors

When you enter midlife, hypothyroidism and perimenopause, along with sleep and stress, can be causes of brain fog. Perimenopause and thyroid-related fog can feel almost identical, so accompanying symptoms matter:

• Perimenopause: Specialists will look for changes in the menstrual cycle, poor sleep, ringing in the ears (tinnitus), and other perimenopausal symptoms.
• Hypothyroidism (underactive thyroid): Additional symptoms to look for include weight gain, constipation and cold intolerance

Medical conditions

Several health conditions can cause brain fog.

• Long COVID and other post-viral illness: Most of us feel a little slow after a cold or the flu. With long COVID and other viral illnesses, that fog can last for weeks, months or longer.
• Autoimmune conditions: Lupus and multiple sclerosis (MS), in which the immune system basically attacks the body, often cause fatigue and brain fog.
• Concussion: Even a mild head injury can lead to cognitive symptoms, like brain fog, that linger.

Medications

Some common medications can cloud your thinking. The main class is anticholinergic medications, which block the action of acetylcholine, a chemical messenger that helps nerve cells communicate with muscles and organs. “And the biggest offenders are Benadryl and medications for urinary incontinence like oxybutynin,” Dr. Lee says. Other medication that can cause brain fog include:

• Some over-the-counter allergy medications
• Anti-anxiety medications such as Xanax, Ativan, and Klonopin
• Sleep aids such as Ambien and Lunesta
• Opioids and some muscle relaxers

If you are trying to ease the brain fog caused by the medication, don’t stop a medication on your own. Talk with your doctor about whether to finish your course or try an alternative.

Age

In your 60s and beyond, brain fog deserves more careful attention. Dr. Lee explains that physicians may evaluate older adults more thoroughly because the chance of a neurological cause — like  Alzheimer’s — increases with age.

When to see a doctor for brain fog

Occasional fog after a poor night’s sleep or a busy week is normal. The key is to determine whether it’s an ongoing pattern. “Persistence, progression, collateral: those are the biggest things that would warrant medical attention,” Dr. Lee explains.

Watch for these signs:

• Persistence: The fog lasts for weeks or months and doesn’t improve on weekends, vacation or after good sleep.
• Progression: Symptoms steadily get worse instead of coming and going.
• Collateral observations: A family member or friend notices changes or worsening in your behavior and expresses concern.

Before your visit, take an honest look at your sleep, alcohol use, stress and mood. Ask someone close to you what they’ve noticed. Then see your primary care specialist, who can check your thyroid, review your medications and screen for related conditions if needed.

Get answers and support

Brain fog is a common experience that many people encounter at some point in their lives. While it often resolves on its own, paying attention to symptoms that persist, worsen or begin to concern those around you is important. Because brain fog can stem from a wide range of causes, including sleep disruption, stress, and underlying neurological conditions, understanding the root cause is key to finding relief. Your primary care specialist is here to help you navigate those complexities, providing the clarity and support you need to move forward with confidence.

Frequently asked questions

What does brain fog feel like?

Most people describe it as thinking through mud. You can still complete tasks, but they require more effort and time than usual.

Can anxiety cause brain fog?

Yes. Anxiety, depression and stress break up your attention and make mental tasks harder. Mood is one of the most common and most treatable contributors.

Brain fog vs. dementia: how can I tell the difference?

Brain fog doesn’t necessarily mean dementia. Many non-neurological factors, like sleep, stress and medications, can cause it. Brain fog caused by dementia tends to persist over longer periods of time, progress and often involves forgetting recent conversations. Family members may notice the changes too.

How do neurologists evaluate brain fog?

A neurologist asks specific questions to see whether a particular thinking skill is affected. They also look for other signs, such as movement problems, hallucinations or behavior changes. Cognitive testing may take a few minutes in a primary care office, or an hour or more with a specialist.

Can brain fog go away?

Often, yes. When the cause is sleep, stress, a recent illness or a medication, brain fog frequently improves once that cause is addressed.