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People with hypothyroidism have an underactive thyroid gland, leading to low thyroid hormone levels in their bodies. Hypothyroidism can occur due to autoimmune conditions such as Hashimoto’s thyroiditis, thyroid surgery, radioiodine therapy (to treat hyperthyroidism), iodine deficiency, or other hereditary conditions. 

Thyroid hormones affect a wide range of bodily functions, including brain development and cognition. Brain fog symptoms are a common patient concern in people with low thyroid function (hypothyroidism). Brain fog represents difficulties with memory, poor concentration, and low energy. Please continue reading to learn more about thyroid-related symptoms that affect the brain.

Can thyroid issues make your head feel weird or spacey?

Thyroid issues can make your head feel “weird” or “spacey.” These are commonly called brain fog symptoms. Surveys have found that nearly 94% of hypothyroid patients report having symptoms associated with brain fog. They include fatigue and cognitive symptoms and can even occur in people taking thyroid hormone replacement therapy for treating hypothyroidism.

One online survey included over 5,000 participants who complained they experienced brain fog while being treated for hypothyroidism. The average age of the participants was around 50 years old; almost all (96%) were women, and about half said Hashimoto’s thyroiditis was the cause of their hypothyroidism (others underwent thyroid surgery or radioactive iodine therapy). Check out our blog: “Hashimoto Disease vs Hypothyroidism: What’s the Difference?”

Nearly 80% of the participants reported experiencing brain fog frequently or all the time. Over half the participants say their brain fog lasts all day. Also, nearly half the participants reported experiencing brain fog symptoms before their hypothyroidism diagnosis. This indicates that brain fog is likely a symptom of thyroid disorder rather than a side effect of thyroid hormone replacement therapy.

The overall combined symptom burden was highest for fatigue, forgetfulness, sleepiness, and difficulty focusing. 

What are the cognitive symptoms of hypothyroidism?

The American Thyroid Association says that hypothyroid symptoms patients associate with brain fog symptoms include:

• Low energy 

• Physical fatigue

• Forgetfulness or memory problems

• Sleepiness

• Difficulty focusing, paying attention, or concentrating

• Mental confusion

• Trouble making decisions

• Cognitive impairment (problems with thinking, learning, remembering, or making decisions and judgments)

• Psychological symptoms and mood disturbances, such as irritability, depressed mood, and anxiety

In most cases, brain fog symptoms and perceived cognitive impairment resolve along with other hypothyroid symptoms with thyroid replacement therapy. However, brain fog symptoms persist in about 10% of patients who receive hypothyroidism treatment with levothyroxine. 

What does thyroid exhaustion feel like?

Thyroid exhaustion can feel different for each person. Members of hypothyroid support groups report the following. Studies have also been done to identify patient concerns related to brain fog in hypothyroidism. They have found these common symptoms participants perceived as brain fog factors:

• I constantly feel tired.

• I feel like I’m walking through sludge.

• I can’t find the right word.

• I can’t articulate what I want to say.

• I have trouble remembering things.

• Reading and understanding things feel like uphill tasks.

• I had to quit my job because I couldn’t think straight. 

• I’ve had to give up work because of physical and mental fatigue.

• Medical professionals dismiss my mood symptoms.

• I get ridiculed for saying my thyroid gland affects cognitive functioning. 

How do doctors manage brain fog in patients with hypothyroidism?

Treating hypothyroidism with thyroid hormone replacement (levothyroxine) is the best way to alleviate symptoms of brain fog. Notably, patients taking thyroid hormone may continue to experience brain fog even after their other hypothyroid symptoms have improved and thyroid stimulating hormone (TSH) levels are in the normal range. Brain fog often does not go away completely, even with carefully monitored thyroid replacement therapy.

The good news is that many people with hypothyroidism report that the following helps improve their brain fog symptoms:

• Adjustment of thyroid hormone replacement (levothyroxine)

• Getting more rest and sleep

• Exercising

• Better nutrition (avoiding gluten, less sugar, less alcohol)

• Staying well hydrated

• More caffeine

• Managing stress

• Less loud noise

• Good patient-doctor relationship

Learn more: “What Are Some Signs My Thyroid Medication Is Not Working?”

Does the type of thyroid hormone replacement affect brain fog symptoms?

The main form of thyroid hormone replacement consists of synthetic lab-made T4 thyroid hormone (levothyroxine). This form of active thyroid hormone has replaced desiccated thyroid extract (DTE) in clinical practice. DTE contains both T4 and T3 thyroid hormones obtained from animal sources. T4 is converted to T3 by the body's peripheral tissues, and most people do not need to take T3 thyroid hormone (liothyronine).

However, a small number of people feel better after transitioning from T4 monotherapy to combination therapy with thyroid extract (T4 and T3). Some studies have found that taking liothyronine (T3 thyroid hormone) can help brain fog symptoms more than desiccated thyroid extract. Check out “What Are the Long-Term Side Effects of Levothyroxine?”

If you have cognitive symptoms or have demonstrated significant functional deficits, talk to your doctor about repeating thyroid function tests. Based on the results, your healthcare professional may adjust your levothyroxine dose, add liothyronine (Cytomel) to your treatment regimen, or recommend taking DTE (NP Thyroid, Armour Thyroid).

What are the symptoms of low thyroid hormone?

According to the National Institute of Diabetes and Digestive and Kidney Disease, the most common symptoms in patients with hypothyroidism (not enough thyroid hormone) include:

• Fatigue

• Weight gain

• Cold intolerance

• Constipation

• Joint pain

• Muscle aches

• Dry skin

• Thinning hair

• Menstrual irregularities

• Fertility problems

• Depression

• Slowed heart rate

• Cognitive dysfunction

What other conditions can cause brain fog symptoms?

A wide range of conditions can affect psychological and neurocognitive function and cause brain fog symptoms. These include lack of sleep, dehydration, medication side effects, depression, sleep apnea, menopause syndrome, vitamin B12 deficiency, chemotherapy treatment, celiac disease, systemic lupus erythematosus, chronic fatigue syndrome, and COVID-19, among others. Learn more about brain fog after COVID.

Persistent symptoms of brain fog are the most frequently reported factor for treatment dissatisfaction in people with hypothyroidism. While it is usually possible to mitigate brain fog with thyroid replacement therapy, these symptoms do not always completely resolve. The chances of reversing brain fog symptoms by treating hypothyroidism are particularly low in patients identified with subclinical hypothyroidism (mildly decreased thyroid function). It is likely that their worsened symptoms of brain fog are due to something other than mild thyroid disease. 

If you have mild hypothyroidism and significant neuropsychiatric symptoms, talk to your doctor about other possible diagnoses. It could be that something other than hypothyroidism is causing brain fog symptoms. 

Doctors can identify patient-reported factors and perform a physical examination and laboratory evaluation to differentiate between thyroid disease (hypothyroidism) and other conditions that can cause brain fog symptoms.