Cortisol and thyroid: how the two are linked and which test to use

Cortisol and thyroid hormones come from different glands and are measured by different blood tests. They are not separate in the body, though. In one small study, higher TSH, the pituitary signal that rises when the thyroid is underactive, went along with higher cortisol, and tiredness can come from either gland. This page covers what that study shows, what it can’t, and which test answers which question.

TSH

One blood test that is a common first check of the thyroid.

$39

See this test at HealthLabs

Price checked November 2026. Not available in ND, RI, NY, NJ, MD and HI. We earn a commission on sales.

How the thyroid and the adrenal glands are related

Both glands take their orders from the pituitary gland at the base of the brain. MedlinePlus says the pituitary makes thyroid-stimulating hormone (TSH), which tells the thyroid how much thyroid hormone to make. It also says the pituitary hormone ACTH tells the adrenal glands how much cortisol to make. When thyroid hormone is low, the pituitary makes more TSH, and when it is high, less. See the HPA axis for the adrenal side.

Each system has its own feedback loop. The study below looks at whether the two systems are related.

Hypothyroidism and cortisol

NIDDK says nearly 5 out of 100 Americans aged 12 and older have hypothyroidism, most cases being mild, and that women are much more likely than men to develop it. Hashimoto’s disease, an autoimmune condition in which the immune system attacks the thyroid, is the most common cause. Fatigue, weight gain, trouble tolerating cold, dry or thinning hair and heavy or irregular periods are among the symptoms. NIDDK also says fatigue and weight gain are common and do not necessarily mean a thyroid problem.

What does the research say about cortisol in this condition? We found one usable study, and it is about people without thyroid disease. In 54 healthy young adults, researchers found that TSH levels from 0.5 to 10 microinternational units per liter were positively linked with cortisol drawn at 1 p.m. Free T3 and free T4 were not linked with cortisol. The authors called their results preliminary and said more research was needed.

It is a small cross-sectional study. It measured people once, so it can’t say which came first.

Hyperthyroidism and cortisol

We found no approved source that shows how an overactive thyroid changes cortisol results, so we don’t make a claim either way. What the government sources do say is about symptoms. NIDDK lists weight loss despite a bigger appetite, a rapid or irregular heartbeat, nervousness, irritability, trouble sleeping, fatigue, sweating and trouble tolerating heat among the symptoms of hyperthyroidism. It says a diagnosis can’t rest on symptoms because many match other diseases, so a clinician uses thyroid blood tests.

Hashimoto’s, Addison’s and cortisol levels

Hashimoto’s disease and Addison’s disease can both be autoimmune. NIDDK says autoimmune disease causes 8 or 9 of every 10 cases of Addison’s disease in developed countries. A 2023 review in Frontiers in Endocrinology says autoimmune adrenal insufficiency is seen alongside other autoimmune disorders in more than 60% of cases, and that autoimmune thyroid disease is one of the conditions clinicians screen for once it is confirmed. In a small series from Poland, 18 of the 34 people with primary adrenal insufficiency who were diagnosed without a crisis also had an autoimmune condition that is part of type 2 autoimmune polyglandular syndrome, and 10 of them had hypothyroidism from Hashimoto’s thyroiditis (Int J Endocrinol, 2013). NIDDK’s hyperthyroidism page lists primary adrenal insufficiency among the conditions that make hyperthyroidism more likely.

The 2023 Frontiers review also says people with primary adrenal insufficiency may have a slightly raised TSH. That is one reason a clinician reads a thyroid result with the whole picture, and why a single abnormal number should not be read alone.

None of this means Hashimoto’s leads to adrenal disease. It means that if you have an autoimmune thyroid condition and also have long-lasting fatigue, muscle weakness, weight loss, loss of appetite or salt cravings, it is worth telling your clinician. NIDDK lists those among the symptoms of adrenal insufficiency. See low cortisol.

Get emergency care now if you have repeated vomiting, severe weakness or fainting. These signs are not a reason to order a test. NIDDK says people with adrenal insufficiency need immediate medical attention if they have a severe infection or diarrhea, or are vomiting and can’t keep steroid pills down. Call 911 or go to the nearest emergency room. See adrenal crisis.

Does cortisol affect the thyroid?

The study above shows that TSH and cortisol move together in one small group of healthy young adults. None of the sources we used shows that cortisol or stress causes thyroid disease, or that a thyroid disease causes a cortisol disorder. If a page tells you that your thyroid problem is caused by your cortisol, that claim isn’t supported here.

Which test answers which question

Your question	Test that usually fits	Who usually arranges it
Is my thyroid under- or overactive?	TSH, often first. An unusual result usually leads to T4, T3 and thyroid antibody tests.	A clinician, or you
Why do I feel tired?	Many possibilities. See tests for tiredness.	A clinician
Is my cortisol low or high?	A morning blood cortisol is a start. Cushing’s syndrome needs other tests. See the cortisol test guide.	A clinician
Is it “adrenal fatigue”?	No test confirms this. It isn’t a recognized diagnosis.	Not applicable

MedlinePlus says a TSH test shows how well the thyroid is working and can tell whether you have too much or too little thyroid hormone. It can’t show why. If a result isn’t normal, a provider will probably order other thyroid blood tests. MedlinePlus says some illnesses unrelated to the thyroid can lower TSH for a short time, that pregnancy affects it, and that TSH can be higher in people over 80 without thyroid disease. If you take thyroid or steroid medicine, don’t change either because of a test result. Ask the prescriber.

The seller’s page for the thyroid panel with TSH lists total T4, T3 uptake, T7 (which it describes as the free thyroxine index), and TSH, and says fasting is not required. Follow the instructions on your lab order. The seller’s TSH page says that test measures TSH only and does not include T3 or T4. Prices for the same type of test vary widely between sellers, and it is worth comparing.

• Thyroid panel with TSHTSH plus other thyroid markers, if your clinician wants more than TSH $59 See this test at HealthLabs
• CortisolCortisol only. Does not measure the thyroid $109 See this test at HealthLabs

Sold by HealthLabs. Prices checked November 2026. Not available in ND, RI, NY, NJ, MD and HI. We earn a commission on sales.

What can change a result

• Estrogen taken by mouth. A review in JBMR Plus says estrogen raises thyroid-binding globulin, the carrier protein for T4 and T3, and a 2023 laboratory review in Diagnostics says oral estrogen raises cortisol’s carrier protein too. Total levels of both can shift without a change in how your glands work. Tell whoever orders the test. See cortisol and birth control.
• Biotin. The FDA says biotin, also called vitamin B7, is used in hormone tests, is found in multivitamins and in products marketed for hair, skin and nails, and can cause falsely high or falsely low results depending on the test. Ask your clinician or the lab whether to pause it before a test. Don’t decide that on your own if a prescriber has told you to take it.
• Time of day. MedlinePlus says cortisol is normally highest in the morning and much lower around 4 p.m., so timing matters for cortisol in a way it does not for most thyroid tests. See AM and PM cortisol timing.

What about “adrenal fatigue”?

Search results for cortisol and the thyroid often lead to “adrenal fatigue”. A 2016 systematic review of 58 studies concluded there is no substantiation that it is an actual medical condition. A 2024 paper in the Journal of the Endocrine Society says it has never been scientifically proven to exist, that its online symptom scores and salivary cortisol profiles have not been validated, and that standard tests are usually normal in people given the label. The same paper says two other labels, Wilson’s syndrome and reverse T3 syndrome, have never been proven to exist either. See adrenal fatigue and fatigue and cortisol.

MedlinePlus says fatigue is a symptom, not a disease, with many causes including thyroid disease, anemia, diabetes, sleep disorders and depression or anxiety. It says to see a provider if tiredness lasts for weeks.

When to see a clinician

See a clinician if tiredness, weight change, temperature intolerance, a fast or slow heartbeat, or changes in your periods have lasted. If you also have weight loss, loss of appetite, muscle weakness or darkening skin, mention that you are worried about your adrenal glands. Don’t start, stop or change thyroid or steroid medicine on your own.