Do Thyroid Disorders Cause Forgetfulness and Brain Fog?

The Effects of Hypothyroidism and Hyperthyroidism on Memory

Thyroid disorders can cause difficulty with energy, concentration, and memory—often described as "brain fog.".

This article explains the link between thyroid function and memory, as well as how hypothyroidism (low thyroid function) and hyperthyroidism (high thyroid function) can mimic the symptoms of dementia.

Forgetfulness and thyroid disorder.

Verywell / Hugo Lin

Thyroid and Memory

Your thyroid gland, which is located in your neck, produces hormones that regulate growth and development. If the thyroid gland is not functioning well, many problems can result. They include extreme fatigue, weight loss or weight gain, rapid heartbeat, and hair loss.

Both hypothyroidism and hyperthyroidism can also cause cognitive problems that can mimic symptoms of mild dementia.

What Is Dementia?

Dementia refers to several conditions that cause a decline in memory and cognitive skills needed to perform the basic activities of daily living. Alzheimer's disease is the most well-known type of dementia.

The early symptoms of dementia can vary from one person to another.

Typical symptoms include:

Symptoms of mild dementia sometimes develop when thyroid levels are abnormal, and they usually resolve with treatment.

Cognitive Symptoms in Hypothyroidism

Women are three times more likely than men to develop hypothyroidism—a medical condition in which the body does not produce enough thyroid hormones.

Cognitive symptoms of people with hypothyroidism include memory problems and difficulty concentrating.

Researchers aren't entirely certain why these issues surface, but they do know that "hypothyroidism affects memory because thyroid hormones play a role in brain areas that are crucial for our memories and cognitive skills." And when production of the thyroid hormone slows down, some people can experience vague symptoms often described as "brain fog."

Small changes in executive functioning have also been noted in untreated or under-treated hypothyroidism. Executive functioning includes abilities such as planning, impulse control, and making decisions.

Cognitive Symptoms in Hyperthyroidism

Hyperthyroidism occurs when your thyroid gland produces more thyroid hormone than your body needs.

Some people with hyperthyroidism, such as Graves' disease, commonly experience poor concentration, slower reaction times, decreased spatial organization, and memory lapses.

Treatment of Thyroid Disease

Fortunately, there are effective treatments available for those with thyroid problems, including medication:

  • People with hypothyroidism are often prescribed levothyroxine, which contains a synthetic hormone to mimic the natural hormone thyroxine.
  • People with hyperthyroidism often take methimazole or propylthiouracil.

These treatments are not curative, and many people take the medication for life.

If you're prescribed one of these pills, the British Thyroid Foundation says there is good reason to be optimistic: "Fortunately, in the great majority of cases, psychological symptoms improve as the thyroid disorder is brought under control by treatment."

Other Interventions for Hyperthyroidism

Certain procedures can treat an overactive thyroid.

  • Radioiodine therapy involves taking radioactive iodine by mouth, either in capsule or liquid form. The treatment slowly destroys the cells of the thyroid gland that produce thyroid hormone, without affecting other body tissues.
  • Surgery can be done to remove part or most of a thyroid gland. Thyroid surgery is a common treatment for thyroid cancer, but it can be an option for non-cancerous thyroid disease as well.

Thyroid Problems and Dementia Risk

Research has shown a complex link between thyroid disease and symptoms of dementia.

  • One study found that participants with subclinical hyperthyroidism (defined as TSH levels lower than 0.10 mIU/L) demonstrated a larger cognitive decline over the course of the research and an increased risk of dementia.
  • Researchers who examined several studies concluded that subclinical hyperthyroidism could be correlated with a risk of dementia; however, they also found that mini-mental state exam (MMSE) scores did not decline any faster with the presence of hyperthyroidism, hypothyroidism, or normal thyroid functioning.
  • A review of 13 different studies found that subclinical hypothyroidism was correlated with increased dementia risk in those who were younger than 75 and in those who had higher TSH levels (a sign of low thyroid hormone).
  • In a post-mortem study of older adults, hypothyroidism that was treated was not found to increase the risk of Alzheimer's brain pathology. This doesn't indicate the actual cognitive functioning of the person, but it does demonstrate that a correlation was not found between actual brain changes of Alzheimer's and thyroid levels.
  • One study found that adequately treated hypothyroidism was not correlated with an increased risk of mild cognitive impairment.

It appears that major cognitive problems are not likely to develop with hyperthyroidism or hypothyroidism. And minor cognitive problems associated with thyroid functioning (like forgetfulness and brain fog) are often temporary and improve with treatment.

In the end, if you're exhibiting major cognitive decline, your healthcare provider should conduct a comprehensive assessment to determine if other medical conditions, besides your thyroid disease, may be contributing to your current state.


It can be embarrassing to appear forgetful. But if you're dealing with a thyroid disorder, you should cut yourself some slack: If your thyroid gland isn’t working properly, it can cause memory issues. Symptoms of both an overactive and underactive thyroid can appear like mild dementia, with poor concentration and memory problems being red flags. The good news is that medication can get both hypothyroidism and hyperthyroidism under control.

A Word From Verywell

If you're experiencing forgetfulness or difficulty concentrating along with your thyroid issues, be sure to alert your healthcare provider. Thyroid problems can cause mild thinking, memory, and concentration issues, and an adjustment of your medications may help. It's also important that you have an evaluation for other potential problems.

Frequently Asked Questions

  • Are thyroid problems linked to an increased risk of dementia?

    Possibly. The research on thyroid and dementia risk is mixed. 

    It appears as though both high and low TSH levels can increase the risk of dementia in people under age 75. However, taking medication to restore thyroid hormone levels to the normal range eliminates the increased risk of dementia. 

  • Is memory loss from hypothyroidism reversible?

    For the most part, yes. Treating hypothyroidism or hyperthyroidism with medications to adjust thyroid levels can help you think more clearly. People who are treated with supplemental thyroid therapy show no decline in cognitive functioning. However, it is unclear if thyroid treatment helps memory issues in adults above age 75.

11 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  2. Alzheimer's Association. What is dementia?

  3. Piedmont Healthcare. The difference between hypothyroidism and hyperthyroidism.

  4. Thyroid Advisor. Hypothyroidism and memory.

  5. British Thyroid Foundation. Psychological symptoms and thyroid disorders.

  6. Medline Plus. Hyperthyroidism.

  7. Juárez-cedillo T, Basurto-acevedo L, Vega-garcía S, et al. Prevalence of thyroid dysfunction and its impact on cognition in older Mexican adults: (SADEM study). J Endocrinol Invest. 2017;40(9):945-952. doi:10.1007/s40618-017-0654-6

  8. Pasqualetti G, Pagano G, Rengo G, Ferrara N, Monzani F. Subclinical hypothyroidism and cognitive impairment: Systematic review and meta-analysis. J Clin Endocrinol Metab. 2015;100(11):4240-8. doi:10.1210/jc.2015-2046

  9. Brenowitz WD, Han F, Kukull WA, Nelson PT. Treated hypothyroidism is associated with cerebrovascular disease but not Alzheimer's disease pathology in older adults. Neurobiol Aging. 2018;62:64-71. doi:10.1016/j.neurobiolaging.2017.10.004

  10. Parsaik AK, Singh B, Roberts RO, et al. Hypothyroidism and risk of mild cognitive impairment in elderly persons: a population-based study. JAMA Neurol. 2014;71(2):201-7. doi:10.1001/jamaneurol.2013.5402

Additional Reading

By Esther Heerema, MSW
Esther Heerema, MSW, shares practical tips gained from working with hundreds of people whose lives are touched by Alzheimer's disease and other kinds of dementia.