High Cortisol vs. Adrenal Insufficiency: What Salivary and Dexamethasone Tests Actually Show

Cortisol is a hormone made by the adrenal glands. It helps regulate blood pressure, blood sugar, metabolism, immune activity, and the body’s response to physical stress. Cortisol levels normally change throughout the day: they are usually highest in the morning and fall to their lowest point around midnight.

Because cortisol is involved in stress, sleep, and many common symptoms, testing can be confusing. Fatigue, weight changes, poor sleep, anxiety, muscle weakness, and changes in blood pressure may occur with many conditions—not only a cortisol disorder.

Two tests often discussed are salivary cortisol testing and the dexamethasone suppression test. They answer different questions. Neither test, by itself, can diagnose every cause of “high cortisol” or rule out adrenal insufficiency.

What does “high cortisol” mean?

A persistently high cortisol level can be caused by Cushing syndrome, a rare medical condition in which the body is exposed to too much cortisol for a prolonged period. Possible causes include:

• A cortisol-producing adrenal tumor
• An ACTH-producing pituitary tumor, sometimes called Cushing disease
• An ACTH-producing tumor elsewhere in the body
• Long-term treatment with steroid medicines, such as prednisone

Symptoms that may occur with Cushing syndrome include:

• Weight gain, especially around the abdomen and face
• Easy bruising and thin skin
• Purple stretch marks, particularly on the abdomen
• Muscle weakness
• High blood pressure or high blood sugar
• Osteoporosis
• Menstrual changes or reduced fertility
• Excess facial or body hair in some women
• Mood changes or difficulty concentrating

Many people with stress, insomnia, depression, obesity, alcohol use disorder, or poorly controlled diabetes can have abnormal cortisol patterns without having true Cushing syndrome. This is sometimes called pseudo-Cushing physiology. It is one reason doctors usually confirm an abnormal screening result with additional testing.

What is adrenal insufficiency?

Adrenal insufficiency occurs when the adrenal glands do not produce enough cortisol. It may be caused by an autoimmune disease affecting the adrenal glands, problems with the pituitary gland, certain medicines, infections, or sudden withdrawal after prolonged steroid treatment.

Symptoms can include:

• Ongoing fatigue and reduced stamina
• Loss of appetite and unintentional weight loss
• Nausea, vomiting, abdominal pain, or diarrhea
• Low blood pressure or dizziness when standing
• Muscle or joint aches
• Salt cravings
• Low blood sugar
• Darkening of the skin, especially in primary adrenal insufficiency

Adrenal insufficiency is not the same as being tired from everyday stress. It is a potentially serious hormone deficiency that requires medical assessment.

What does a salivary cortisol test show?

Salivary cortisol testing measures the amount of free cortisol in saliva. “Free” means the hormone is not attached to a blood protein and may better reflect the biologically available cortisol at that moment.

The most established use is late-night salivary cortisol. In healthy people, cortisol should be very low late at night. In many people with Cushing syndrome, this normal nighttime drop is lost. Doctors may ask for one or more saliva samples collected at home, usually close to bedtime.

Late-night salivary cortisol can help screen for excess cortisol when:

• The sample is collected at the correct time
• The person has a regular sleep schedule
• The collection instructions are followed carefully
• The result is interpreted using the laboratory’s reference range

However, saliva testing has important limitations. Results may be affected by:

• Shift work or irregular sleep
• Recent eating, drinking, brushing, or flossing
• Blood from irritated or bleeding gums
• Smoking or nicotine use
• Contamination from steroid creams, inhalers, or other medicines
• Acute illness, severe stress, or disrupted sleep
• Certain laboratory collection and assay methods

A single abnormal result does not prove Cushing syndrome. Doctors may repeat the test or use a different screening method, such as a 24-hour urine free cortisol test or a low-dose dexamethasone suppression test.

Salivary cortisol is not usually the main test for adrenal insufficiency. Commercial “adrenal fatigue” saliva panels may report daily cortisol patterns, but “adrenal fatigue” is not a recognized medical diagnosis, and these panels cannot reliably diagnose adrenal insufficiency. If adrenal insufficiency is suspected, blood testing and an ACTH stimulation test are generally more appropriate.

What does the dexamethasone suppression test show?

Dexamethasone is a synthetic steroid that acts like cortisol. Normally, taking a small dose should signal the brain and pituitary gland to reduce ACTH production. Lower ACTH should then cause the adrenal glands to reduce their cortisol output.

In an overnight low-dose dexamethasone suppression test, a person takes dexamethasone late at night. A blood cortisol level is measured the next morning.

• Normal response: cortisol becomes very low or adequately suppressed.
• Abnormal response: cortisol remains higher than expected, suggesting possible autonomous cortisol production.

This test is mainly used to screen for Cushing syndrome. It may also be used when an adrenal nodule is found on imaging, to check whether the nodule is producing cortisol without normal hormonal control.

An abnormal dexamethasone suppression test does not identify the exact cause of excess cortisol. Further tests may include ACTH measurement, repeat cortisol testing, or imaging. The result must also be interpreted in context because several factors can produce misleading results.

These include:

• Medicines that speed up or slow down dexamethasone breakdown
• Some anti-seizure medicines, rifampin, and certain other drugs
• Estrogen-containing birth control or hormone therapy, which can affect total blood cortisol
• Vomiting or failure to absorb the tablet
• Liver or kidney disease
• Alcohol use disorder, depression, severe obesity, or acute illness
• Incorrect timing or laboratory differences

Patients should tell the clinician about all prescription medicines, supplements, inhaled steroids, skin creams, injections, and birth control before testing. They should not stop prescribed medicine without medical advice.

How are these tests different from adrenal insufficiency testing?

A dexamethasone suppression test asks whether cortisol can be turned down when it should be. It is designed to investigate excess cortisol and is not a standard test for adrenal insufficiency.

For suspected adrenal insufficiency, doctors commonly begin with:

• An 8 a.m. blood cortisol, taken when cortisol should normally be near its daily peak
• An ACTH blood level, which helps distinguish primary from central adrenal insufficiency
• An ACTH stimulation test, also called a cosyntropin stimulation test

During an ACTH stimulation test, synthetic ACTH is given and cortisol is measured before and after the dose. A healthy adrenal response is expected to produce a sufficient rise in cortisol. The precise cutoff depends on the laboratory, testing method, and clinical situation.

A morning cortisol that is clearly low can support adrenal insufficiency, while a clearly adequate result may make it less likely. Intermediate results usually require additional testing. Recent steroid treatment can interfere with evaluation, so the testing plan should be arranged by a clinician.

Which test is right?

The best test depends on the medical question:

• Possible Cushing syndrome: late-night salivary cortisol, 24-hour urine free cortisol, or overnight dexamethasone suppression testing may be used.
• Possible adrenal insufficiency: morning blood cortisol, ACTH, and often an ACTH stimulation test are more relevant.
• An abnormal screening result: repeat or confirmatory testing is often needed before making a diagnosis.
• Unexplained symptoms alone: testing should be guided by an examination and medical history, rather than by symptoms such as tiredness in isolation.

If you are unsure how concerning your symptoms may be, you might consider a free, online symptom check, using the doctor approved Ubie Symptom Checker. It cannot diagnose a cortisol disorder, but it may help you organize symptoms and decide what to discuss with a healthcare professional.

When to seek urgent medical help

Speak to a doctor about persistent symptoms, unexplained weight or blood pressure changes, abnormal test results, or any concern about cortisol or adrenal function.

Seek urgent care for severe vomiting or diarrhea, fainting, confusion, extreme weakness, severe dehydration, very low blood pressure, or inability to keep fluids down. These can be signs of an adrenal crisis or another serious illness. Anyone with potentially life-threatening or rapidly worsening symptoms should seek emergency medical help rather than waiting for a home test or routine appointment.