COVID-19 can affect thyroid function in several ways, though most thyroid disruptions that occur during or after infection resolve on their own. The virus doesn’t appear to directly invade thyroid cells, but it can trigger inflammation in the gland, temporarily suppress thyroid hormone production during severe illness, and in rarer cases, set off autoimmune thyroid conditions like Graves’ disease or Hashimoto’s thyroiditis.
How the Virus Affects the Thyroid
The thyroid gland’s main hormone-producing cells, called follicular cells, don’t carry the two surface proteins (ACE2 and TMPRSS2) that the virus uses to enter human cells. That means SARS-CoV-2 likely can’t directly infect the thyroid the way it infects lung or heart tissue. However, a 2022 study published in Biology found that ACE2 is present on pericytes, the tiny cells that wrap around blood vessels inside the thyroid. When the virus infects these pericytes, it can damage the gland’s blood supply and trigger inflammation that spills over into surrounding thyroid tissue.
This indirect route of damage helps explain why thyroid problems after COVID tend to be inflammatory rather than destructive, and why most people recover full thyroid function within a few months.
Subacute Thyroiditis After COVID
The most well-documented thyroid complication is subacute thyroiditis, a painful inflammation of the thyroid gland. A systematic review in Frontiers in Endocrinology examined 100 patients across 43 published reports who developed this condition after COVID. Symptoms appeared an average of 28 days after infection, though the range was wide, from the same day out to nearly six months later.
The hallmark symptom is neck pain, reported by 69% of patients. The pain is typically felt on one or both sides of the neck and can radiate to the ear, jaw, or under the chin. Other common symptoms included fever (54%), fatigue (34%), and persistent palpitations (31%). A smaller number of patients experienced anxiety, irritability, or mood changes, likely driven by the temporary surge in thyroid hormones that occurs when an inflamed gland leaks its stored supply into the bloodstream.
During the initial inflammatory phase, thyroid hormone levels spike while TSH (the brain’s signal telling the thyroid to work) drops very low. In the reviewed cases, TSH fell to an average of 0.08 mIU/L, well below normal. Ultrasound typically showed dark (hypoechoic) patches in 79% of patients and an enlarged gland in 50%.
About 23% of these patients eventually swung into a hypothyroid phase, where the gland temporarily underperforms after the inflammation burns out. Only a fraction of those needed thyroid hormone replacement medication. Most recovered without it.
Thyroid Suppression During Severe Illness
Hospitalized COVID patients frequently show a pattern called sick euthyroid syndrome, where the body deliberately dials down thyroid hormone levels as a response to critical illness. This isn’t unique to COVID; it happens with pneumonia, sepsis, heart attacks, and other serious conditions. But the rates in COVID are notably high, with studies finding it in up to 64% of hospitalized patients.
The pattern involves low levels of the active thyroid hormone (free T3) with relatively preserved or slightly elevated levels of free T4. A population-level study found that the combination of low free T3 and elevated free T4 was 3.6 times more common during the first COVID wave compared to reference periods. This hormonal shift appears to carry prognostic weight: patients in the lowest third for free T3 levels had a 40% mortality rate compared to about 6% in those with higher levels.
This doesn’t mean low thyroid hormones caused worse outcomes. Rather, the degree of thyroid suppression reflects how severely the body is stressed. These levels typically normalize as the patient recovers, without any thyroid-specific treatment.
Autoimmune Thyroid Disease
A smaller but clinically significant group of patients develop new autoimmune thyroid conditions after COVID. A 2024 review in Cureus documented 28 cases of Graves’ disease either newly triggered or relapsed after SARS-CoV-2 infection, reported between 2020 and early 2024. Several cases of new-onset Hashimoto’s thyroiditis were also identified, appearing roughly one to two months after infection.
The mechanism is thought to involve immune system dysregulation rather than direct viral damage. COVID triggers a massive immune response, and in some people, particularly those with a genetic predisposition, this response misfires and begins attacking the thyroid. In Graves’ disease, the immune system produces antibodies that overstimulate the thyroid, causing hyperthyroidism. In Hashimoto’s, the attack gradually destroys thyroid tissue, leading to hypothyroidism.
These cases remain relatively rare compared to the billions of COVID infections worldwide. But for someone who develops unexplained thyroid symptoms weeks after recovering from COVID, particularly a racing heart, weight changes, heat or cold intolerance, or unusual fatigue, the connection is worth investigating with a simple blood test.
How Long Thyroid Problems Last
The reassuring finding across multiple studies is that most COVID-related thyroid dysfunction is temporary. In a follow-up study of 204 patients, 43 had abnormal thyroid function during their acute infection. Of those, 81.4% had completely normal levels by the follow-up assessment, which occurred at a median of 89 days (roughly three months) after infection. All patients who had mildly abnormal free T4 or free T3 levels during acute illness normalized without treatment.
Subacute thyroiditis follows a similar trajectory. The inflammatory phase lasts weeks, sometimes followed by a temporary hypothyroid dip, with most patients returning to normal thyroid function within two to three months. The subset who develop true autoimmune conditions like Graves’ or Hashimoto’s are the exception: these tend to be chronic and require ongoing management, just as they would if triggered by any other cause.
COVID Vaccination and Thyroid Risk
Some people have wondered whether COVID vaccines carry the same thyroid risks as the infection itself. A large population-based study covering 3 million individuals found no association between the mRNA COVID vaccine and subacute thyroiditis at 30, 60, or 90 days after vaccination. Notably, the same study also found no statistically significant association between COVID infection itself and subacute thyroiditis at the population level, after adjusting for age and sex. This suggests that while individual cases clearly occur and are well-documented in case reports, the overall population-level risk remains low for both infection and vaccination.
Symptoms Worth Paying Attention To
If you’ve had COVID and notice new symptoms in the weeks or months afterward, some patterns point toward thyroid involvement:
- Neck pain or tenderness, especially if it radiates to your jaw or ears, suggests possible subacute thyroiditis.
- Racing heart, tremor, weight loss, or heat intolerance could indicate a hyperthyroid phase, either from thyroiditis or new-onset Graves’ disease.
- Unusual fatigue, weight gain, cold sensitivity, or brain fog that persists beyond typical post-COVID recovery may point to hypothyroidism.
A standard thyroid panel (TSH, free T3, and free T4) is all that’s needed to screen for these problems. There are currently no formal guidelines recommending routine thyroid screening after every COVID infection, but testing is straightforward and inexpensive when symptoms suggest something is off.