Do Thyroid Disorders Cause Forgetfulness and Brain Fog?

The Effects of Hypothyroidism and Hyperthyroidism on Memory

Do you feel like you're forgetting things more often or as though your brain is clouded in fog?

Memory loss has many triggers, and some are related to Alzheimer's disease or other dementias. Others are due to potentially reversible causes, one of which is a thyroid disorder.

This article explains the link between thyroid and memory as well as how the thyroid disorders of hypothyroidism and hyperthyroidism can mimic the symptoms of dementia. It also identifies the medications that are often used to treat thyroid disorders, as well as two more aggressive options.

Forgetfulness and thyroid disorder.

Verywell / Hugo Lin

Thyroid and Memory

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

Both hypothyroidism (an "underactive" thyroid) and hyperthyroidism (an "overactive" thyroid) can also cause cognitive problems that can mimic symptoms of mild dementia.

What Is Dementia?

Dementia is a blanket term that refers to not one but several conditions that cause a loss in memory and other cognitive skills needed to perform the basic activities of daily living. Alzheimer's disease is probably the most well-known type of dementia.

The way in which dementia "presents" itself varies from one person to another. But a person with dementia typically exhibits at least two of the following symptoms:

Symptoms of mild dementia sometimes develop when thyroid levels are abnormal, but generally appear to 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 of the thyroid hormone.

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, people feel it "via 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 (also called Graves' disease) commonly exhibit poor concentration, slower reaction times, decreased spatial organization, and memory lapses.

Thyroid Pills Can Help

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

  • People with hypothyroidism are often prescribed levothyroxine. The sodium tablet contains a synthetic hormone to mimic thyroxine, which the thyroid gland produces naturally.
  • People with hyperthyroidism often take methimazole or propylthiouracil. Neither provides a cure, with many people taking 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."

Two Other Treatment Options

Thyroid medication may be the simplest treatment, but two other tactics can moderate an under- or overactive thyroid:

  • Radioiodine therapy involves taking radioactive iodine by mouth, either in capsule or liquid form. The treatment slowly but surely destroys the cells of the thyroid gland that produce thyroid hormone. (It leaves other body tissues alone).
  • Surgery can be done to remove part or most of a thyroid gland. Thyroid surgery is a last-resort move, though it may be a good option for pregnant women, for instance, who cannot take thyroid medication.

Thyroid Problems and Dementia Risk

Several researchers have questioned whether hyperthyroidism or hypothyroidism increases the risk for dementia to develop. Findings on this question include the following:

  • 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. There was no increased risk in those with less significant thyroid stimulating hormone (TSH) levels. Too much TSH can signal hyperthyroidism while too little can point to hypothyroidism.
  • Researchers also took a look at several studies on thyroid function and cognition. They 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.
  • Another review of 13 different studies found that subclinical hypothyroidism was correlated with an increased dementia risk in those who were younger than 75 and in those who had higher TSH levels.
  • 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.
  • Yet another study found that hypothyroidism was not correlated with an increased risk of mild cognitive impairment. The researchers note that these results assume that hypothyroidism had been treated and thus there does not appear to be any long-term effects on cognitive functioning.

In short, while research findings can be inconsistent, 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.

In the end, if you're exhibiting major cognitive decline, your healthcare provider should conduct a comprehensive assessment to determine if other medical conditions 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 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. While you might initially feel embarrassed or uncomfortable about your brain fog, remind yourself that sharing this knowledge with your healthcare provider empowers both of you as work toward the goal of restoring your normal functioning.

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.

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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.
  1. Cooke GE, Mullally S, Correia N, et al. Hippocampal volume Is decreased in adults with hypothyroidism. Thyroid. 2014;24(3):433-440. doi:10.1089/thy.2013.0058

  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

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