Understanding Brain Fog in Hypothyroidism

brain fog and confusion are symptoms of thyroid

Some people with an overtly underactive thyroid gland (hypothyroidism) report cognitive problems, often referred to as "brain fog." 

While "brain fog" is not a medical term, per say, it has become a well-recognized description of a group of symptoms that may include:

  • Difficulty concentrating
  • Short-term and long-term memory problems
  • Forgetfulness
  • Lack of focus
  • Feeling "spaced out"
  • Confusion
  • Difficulty with clear thinking
  • Feeling inexplicably anxious or irritable
  • Feeling tired and unmotivated

Your brain requires sufficient levels of thyroid hormone in order to function properly. So it's no surprise that a symptom like brain fog is often reported by patients who have hypothyroidism. The good news is that with treatment of your underactive thyroid, "brain fog" generally resolves—a great and often dramatic relief.

However, some people continue to report "brain fog," despite normal TSH levels, according to a study in the journal Thyroid. 

That said, the authors of the study "Psychiatric and Cognitive Manifestations of Hypothyroidism" could not find a correlation between a person's thyroid function and certain cognitive abilities, like attention or concentration. This finding supports traditional thyroid care, which is that doctors often do not alter thyroid hormone doses in people with hypothyroidism (who have normal TSH) and who complain solely about cognitive problems.

Interestingly, though, the study did find a link between thyroid function and "real life" decisions. The authors found that people with low-normal TSH levels made more advantageous decisions than people with high-normal TSH levels on the Iowa Gambling Task (a test that mimics real-life decision making)  

The take-home message here is that your "brain fog" could be related to subtle changes within your thyroid function (especially when it comes to achieving more complex tasks like making decisions), but we simply do not have enough sophisticated tests to tease this all out yet.

Until then, doctors are not likely to alter your dose (if your TSH is normal) based on "brain fog," alone; although this is not a hard and fast rule, as your doctor will access each person differently. 

Brain Fog Causes Besides Your Thyroid 

It's important to note that your "brain fog," may not be related to your thyroid. In fact, there could be an entirely unique culprit behind it.

Examples of other potential causes of brain fog include:

  • Iron deficiency anemia
  • Sleep disorder
  • Depression
  • Nutritional deficiencies
  • Excessive carbohydrate intake
  • Another autoimmune disease (for example, celiac disease)

A Word From Verywell

If you have brain fog or other potential thyroid symptoms and are not diagnosed or treated, your first step is to see your physician for a complete thyroid evaluation.

If you are a person with diagnosed hypothyroidism experiencing brain fog, you should first discuss this with your physician. In addition to ordering thyroid blood tests, your doctor may evaluate you for other possible causes.



Samuels MH. Psychiatric and cognitive manifestations of hypothyroidism. Curr Opin Endocrinol Diabetes Obes. 2014 Oct;21(5):377-83.

Samuels MH, Kolobova I, Smeraglio A, Niederhausen M, Janowsky JS, Schuff KG. Effect of thyroid function variations within the laboratory reference range on health status, mood, and cognition in levothyroxine-treated subjects. Thyroid. 2016 Sep 1;26(9):1173-84.