Brain Fog, Fatigue, and Cognitive Concerns in Hypothyroidism

tired man touching neck, thyroid
Numerous people on thyroid replacement therapy for hypothyroidism describe symptom such as persistent ‘brain fog.’ Researchers aimed to better understand what other issues ‘brain fog’ may be related to.

A research team at the University of Chicago investigated descriptions of persistent brain fog from individuals with hypothyroidism, even with thyroid hormone replacement treatment, and discovered it was also frequently related to fatigue and cognition symptoms. The results were published in Endocrine Practice.

The study analyzed the survey responses of 5170 people with hypothyroidism (95.9% women) who answered an online survey conducted between September 15 and October 26, 2020. Participants were asked to identify the cause of their hypothyroidism if known, such as Hashimoto Thyroiditis, thyroid surgery, treatment with radioactive iodine, or a combination of these. The 10-question survey asked patients’ perspectives on the cause, frequency, duration (including time of day), and definition of brain fog. Patients rated the frequency of other symptoms coinciding with brain fog and the degree to which brain fog interfered negatively with function. Additionally, patients described in their own words what they perceived made their brain fog better or worse.

Following textual data analysis of the survey responses, the investigators calculated that 2409 (46.6%) individuals reported brain fog prior to their hypothyroidism diagnosis and 4096 (79.2%) experienced brain fog frequently or all the time. More than half of the respondents (56.4%) stated their brain fog lasted all day while the remaining individuals reported less brain fog in the evening. Fatigue and forgetfulness were commonly reported with brain fog.

More than 95% of respondents listed fatigue, forgetfulness, sleepiness, and lack of focus as the most common symptoms coinciding with brain fog, stating these symptoms  commonly impacted their lives in a negative way. Lifestyle modifications that improved brain fog and associated symptoms included rest (51.7%), thyroid hormone replacement dosage adjustments (28.3%), and exercise (10.4%). Liothyronine (LT3) supplementation improved brain fog symptoms more so than desiccated thyroid extract (8.3% vs 4.0%).

The study authors noted several limitations. Participants were a nonrandom sample of people who self-reported having hypothyroidism with brain fog symptoms and who had regular access to hypothyroidism-related websites where the survey was posted, which investigators considered a form of selection bias. The survey was also designed to be minimally burdensome to encourage maximum participation, so it did not include medical information to confirm the diagnosis of hypothyroidism.

In addition to hypothyroidism, chronic fatigue syndrome, chemotherapy, postural orthostatic tachycardic syndrome, and aging may contribute to brain fog and related symptoms, according to the investigators. Approximately 46% of survey respondents claimed they experienced brain fog prior to a diagnosis of hypothyroidism, implying other conditions may potentially have influenced symptoms.

“The present study characterizes brain fog from the perspective of patients with hypothyroidism as an array of symptoms that represent a significant cognitive and functional burden on daily life” the authors stated. “Exploring…new areas of patient concern may provide a new pathway through which to approach the experience of patients with hypothyroidism, in addition to the traditional thyroid-specific symptom approach,” they concluded.

Disclosure: One study author declared affiliations with private industry. Please see the original reference for a full list of authors’ disclosures.


Ettleson MD, Raine A, Batistuzzo A, et al. Brain fog in hypothyroidism: understanding the patient’s perspective. Endocr Pract. Published online December 8, 2021. doi:10.1016/j.eprac.2021.12.003