Do Thyroid Disorders Cause Forgetfulness and Brain Fog?

The Effects of Hypothyroidism and Hyperthyroidism on Memory

How the Thyroid Can Affect Memory
AG Holesch/Image Broker/Getty Images

Feeling like you're forgetting things more often, or your brain is in a fog? There are many causes of memory loss, and while some are related to Alzheimer's disease or other dementias, others are due to potentially reversible causes, one of which is a thyroid disorder.

What Is the Thyroid?

The thyroid is a gland in your neck that produces hormones that regulate growth and development. But, if it's not functioning well, problems with the thyroid can cause many challenges including extreme fatigue, weight loss or gain, rapid heartbeat, and hair loss. Interestingly, both hypothyroidism and hyperthyroidism can also cause cognitive problems that can mimic symptoms of mild dementia.

What Is Dementia?

Many people incorrectly think that dementia is some specific type of disease. However, dementia is a blanket term which refers to a decrease in memory and other cognitive skills needed to perform routine activities of daily living.

Alzheimer's disease is just one form of dementia, and according to the Alzheimer's Association, it accounts for 60 to 80 percent of all cases of dementia. Another common cause of dementia is vascular dementia which occurs after a stroke, or when blood supply to the brain is compromised.

The presentation of dementia varies from one person to another. Nevertheless, a person with dementia presents with at least two of the following symptoms:


Hypothyroidism is a medical condition where not enough of the thyroid hormone is being produced. People with low thyroid levels may feel tired, gain weight, and experience dry, itchy skin and constipation.

Cognitive symptoms of people with hypothyroidism include memory problems and difficulty concentrating. Research has shown that verbal memory in particular may be affected by hypothyroidism. Another study found decreased hippocampal volume in adults with untreated hypothyroidism.

Small changes in executive functioning have also been noted in untreated or under-treated hypothyroidism. Executive functioning can include abilities such as planning, impulse control and making decisions. It's important to note, however, that larger changes in executive functioning are likely not related to hypothyroidism and thus should be reported to the physician.


Hyperthyroidism is when too much of the thyroid hormone is produced. Symptoms may include feeling jittery, unintended weight loss, and heart flutters.

Some people with hyperthyroidism (also called Graves disease) commonly exhibit poor concentration, slower reaction times, decreased spatial organization and decreased visual processing skills.

Prevalence of Thyroid Disorders

It's estimated that 200 million people worldwide suffer from a thyroid disorder, although it's difficult to know for certain because many go undetected. We do know that as people age, it's more likely that they'll develop a thyroid disorder; however, many younger adults develop thyroid problems as well.


Fortunately, there is an effective treatment available for those with thyroid problems. The thyroid hormone levels can be adjusted through the use of oral medications, radioactive iodine, and/or surgeries.

So, can this treatment help people with thyroid disorders who are experiencing cognitive problems? Although there is some question of the effectiveness of treatment with significantly older adults, most research shows that cognitive functioning improves when thyroid disorders are treated.

In fact, according to the Rancho Bernardo study, people who've been treated with supplemental thyroid therapy show no decline in cognitive functioning.

A Word From Verywell

If you're experiencing forgetfulness or difficulty concentrating along with your thyroid concerns, be sure to convey these issues to your physician. While you might initially feel embarrassed or uncomfortable about your brain fog, remind yourself that sharing this knowledge with your doctor helps the two of you be more effective as you work towards the goal of restoring your normal functioning. 

Was this page helpful?
Article Sources
  • American Thyroid Association. Thyroid Disease in Older Patients.
  • Cooke GE, Mullally S, Correia N, et al.  Hippocampal Volume Is Decreased in Adults with Hypothyroidism. Thyroid. 2014;24(3):433-440.
  • European Journal of Endocrinology. December 1, 2009 161 917-921. Treated hypothyroidism, cognitive function, and depressed mood in old age: the Rancho Bernardo Study.
  • International Journal of Neuroscience. 116:895-906, 2006. Memory Improvement with Treatment of Hypothyroidism.
  • The Journal of Neuropsychiatry and Clinical Neurosciences, VOL. 19, No. 2. Verbal Memory Retrieval Deficits Associated With Untreated Hypothyroidism.
  • Samuels, M. (2014). Psychiatric and cognitive manifestations of hypothyroidism.Current Opinion in Endocrinology & Diabetes and Obesity, 21(5), pp.377-383.