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What is cortisol?

Cortisol is the main stress hormone produced by your adrenal glands and is involved in the “fight or flight” response. It affects energy levels, blood pressure, digestion, and your sleep/wake cycle. 

What does cortisol test for?

Chronic stress can lead to high cortisol levels and is known to affect heart health¹ and stress is known as a long-term risk factor for high blood pressure or hypertension². Abnormal levels of cortisol—either too high or too low—could indicate Cushing’s syndrome or Addison’s disease. Healthcare professionals may need to conduct additional tests to determine the cause of abnormal levels of cortisol.

The cortisol test measures whether your cortisol levels are high or low, which may be a sign of an adrenal gland condition or that lifestyle changes need to be made.

When should I test my cortisol levels?

You should test cortisol levels if you have symptoms of either low or high cortisol. High levels can affect your heart rate and energy levels.

Symptoms of Addison’s disease (low cortisol) include extreme fatigue, weight loss, darkening of the skin, low blood pressure (which may cause fainting), and more³. Levels of ACTH, the hormone that stimulates the production of cortisol, can be either elevated or decreased, depending on the cause of low cortisol. Other tests may be needed to diagnose this disease.

Symptoms of Cushing syndrome (high cortisol) include obesity, high blood pressure, and elevated blood glucose levels⁴.


What is a normal cortisol level?

Reference values vary according to the time of day the test is taken and may vary between labs. Normally, they are highest in the early morning and decrease in the evening.

  • 8:00 AM, 5–23 µg/dL
  • 4:00 PM, 3–16 µg/dL

A person’s normal levels of cortisol can be elevated by acute stress, alcoholism, depression, prescription drugs, pregnancy, and estrogen therapy.

What does a low level of cortisol mean?

Lower than normal levels of cortisol could be indicative of Addison’s disease, hypopituitarism, or adrenal insufficiency.

What does a high level of cortisol mean?

The most common cause of elevated cortisol levels in women is a high level of estrogen in the blood due to pregnancy or estrogen therapy. Excess levels of cortisol can also be indicative of Cushing syndrome, which is a rare disorder. The most common cause of Cushing syndrome is the use of corticosteroids, though it can also be caused by overproduction of the hormone ACTH. 


How can I lower my cortisol levels?

Cortisol levels may be lowered by changing the medications you’re taking in consultation with your healthcare professional. If chronic stress is the cause of elevated cortisol, you may benefit from getting adequate sleep, exercising regularly, eating a healthy diet, and reducing the amount of caffeine you drink. 


  1. Levine GN, Cohen BE, Commodore-Mensah Y, et al. Psychological Health, Well-Being, and the Mind-Heart-Body Connection: A Scientific Statement From the American Heart Association. Circulation 2021;143(10):e763-e783.
  2. Ming EE, Adler GK, Kessler RC, et al. Cardiovascular reactivity to work stress predicts subsequent onset of hypertension: the Air Traffic Controller Health Change Study. Psychosom Med 2004;66(4):459–465.https://journals.lww.com/psychosomaticmedicine/Abstract/2004/07000/Cardiovascular_Reactivity_to_Work_Stress_Predicts.1.aspx 
  3. Mayo Clinic. Addison’s disease. Available from: https://www.mayoclinic.org/diseases-conditions/addisons-disease/diagnosis-treatment/drc-20350296
  4. Mayo Clinic Laboratories. Test ID: CORT. Cortisol, serum. Available from: https://www.mayocliniclabs.com/test-catalog/Clinical+and+Interpretive/8545
  5. McGee S. 2018. Evidence-Based Physical Diagnosis. Elsevier. Chapter 14, Cushing Syndrome; p. 89–94.e2. 
  6. Fischbach FT, Dunning MB III, eds. 2009. Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
Last updated:
September 23, 2021

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