Clinical Thyroidology® for the Public

Summaries for the Public from recent articles in Clinical Thyroidology
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Hypothyroid patients described what brain fog feels like

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Hypothyroidism is common and is diagnosed with increased TSH and low FT4 levels. Common symptoms of hypothyroidism include feeling tired, cold, and sluggish along with weight gain, dry skin and constipation. These symptoms often resolve on thyroid hormone replacement therapy and return of the FT4 and TSH back to the normal range.

One particular symptom that patients often report is brain fog, which is described as a group of symptoms including low energy, forgetfulness, sleepiness and difficulty focusing. Interestingly, while this symptom is frequently reported in patients with hypothyroidism, it is also reported by patients with other medical conditions, such as lupus, chronic fatigue syndrome, COVID-19 (“long COVID”) and depression. Because brain fog is not specific to one particular medical problem, it is difficult to manage. Indeed, brain fog may persist after the other symptoms of hypothyroidism resolve on thyroid hormone therapy.

This study was done to better understand the symptoms associated with brain fog in patients with hypothyroidism, to find out how often it occurs and to determine what improves the symptoms commonly experienced in patients who suffer from brain fog.

Ettleson MD et al 2021 Brain fog in hypothyroidism: Understanding the patient’s perspective. Endocr Pract. Epub 2021 Dec 8. PMID: 34890786

A questionnaire was sent online to patients with hypothyroidism who were in the American Thyroid Association database and participate in hypothyroid support groups. Patients over 16 years-old who experience brain fog in spite of treatment were included in the study. Patients were asked what was the cause of their hypothyroidism, how often the symptom presented, what time of the day, what made it better and what other symptoms were present when feeling brain fog.

Over 5000 people who complained of brain fog while being treated for hypothyroidism participated in this study. The average age was about 50 years-old, almost all were women and about half had Hashimoto’s thyroiditis as the cause of their hypothyroidism. Most participants reported having brain fog very frequently or all the time and about half reported having this symptom before the diagnosis of hypothyroidism. Over 95% of the patients reported having fatigue, forgetfulness, sleepiness and difficulty focusing when experiencing brain fog. Rest and exercise alleviated the symptoms. A small number of participants felt better when liothyronine (L-T3) was added to their levothyroxine treatment, but the improvement was a bit more common in those over 50 years old. Also, patients reported that the relationship between the patient and their doctor was particularly important in the management of brain fog.

Brain fog in hypothyroid patients was associated most frequently with fatigue, forgetfulness and difficulty focusing and often persists after normalization of the thyroid hormone levels and negatively impacts patients’ lives. Important in managing patients with brain fog includes a supportive doctor-patient relationship and willingness to consider additional treatment, including adding liothyronine to the treatment regimen. In addition, lifestyle changes like more rest and exercise can help. More research is needed to better understand the relationship between brain fog and hypothyroidism and to improve current treatment regimens.

— Susana Ebner MD


Hypothyroidism: a condition where the thyroid gland is underactive and doesn’t produce enough thyroid hormone. Treatment requires taking thyroid hormone pills.

Hashimoto’s thyroiditis: the most common cause of hypothyroidism in the United States. It is caused by antibodies that attack the thyroid and destroy it.

Levothyroxine (T4): the major hormone produced by the thyroid gland and available in pill form as Synthroid™, Levoxyl™, Tirosint™ and generic preparations.

Triiodothyronine (T3): the active thyroid hormone, usually produced from thyroxine, available in pill form as Liothyronine or Cytomel™.

Thyroid hormone therapy: patients with hypothyroidism are most often treated with Levothyroxine in order to return their thyroid hormone levels to normal. Replacement therapy means the goal is a TSH in the normal range and is the usual therapy. Suppressive therapy means that the goal is a TSH below the normal range and is used in thyroid cancer patients to prevent growth of any remaining cancer cells.

May is International Thyroid Awareness Month