Cortisol Morning Test: Normal Levels, High & Low Causes

A 45-year-old woman walks into my clinic complaining of fatigue, unexplained weight gain around her abdomen, and difficulty sleeping. Her blood pressure is elevated. One of the first tests I order is a morning cortisol level. This simple blood draw, taken between 7 and 9 a.m., can give us a remarkable window into how her adrenal glands and pituitary gland are working. In my practice, I’ve seen morning cortisol uncover everything from chronic stress to hidden tumours. Here’s what you need to know.

What Is a Morning Cortisol Test?

Cortisol is a steroid hormone produced by the adrenal glands. It follows a natural 24-hour rhythm: levels peak in the early morning (around 8 a.m.) and trough around midnight. The morning cortisol test measures this peak level. It is formally coded under LOINC 2142-1 (Cortisol [Mass/volume] in Serum or Plasma – morning).

This test is used to screen for disorders of the adrenal glands and pituitary, such as Cushing’s syndrome (high cortisol) or Addison’s disease (low cortisol). It also helps monitor patients on long-term glucocorticoid therapy.

Reference Ranges for Morning Cortisol

Normal ranges can vary slightly between laboratories. The values below are typical for a morning (8 a.m.) sample in adults and children.

Note: Pregnant women, individuals on oral contraceptives, and those taking corticosteroids may have different ranges. Always interpret results with your doctor.

What Does High Morning Cortisol Mean?

When morning cortisol is elevated, we first consider whether it's a temporary spike due to stress, acute illness, or intense exercise. But if levels remain high, further testing is needed.

Possible Causes of High Cortisol

• Cushing’s syndrome – often from a pituitary tumour (Cushing’s disease) or adrenal tumour
• Chronic stress or depression – prolonged activation of the HPA axis
• Alcoholism – can mimic Cushing’s syndrome
• Medications – such as corticosteroids, some anticonvulsants, or oestrogen
• Pregnancy – cortisol normally rises in the third trimester

My patients often ask, “Is high cortisol dangerous?” Yes, persistently high cortisol can lead to obesity, diabetes, osteoporosis, and cardiovascular disease. That’s why we investigate thoroughly.

What Does Low Morning Cortisol Mean?

A low morning cortisol level suggests the adrenal glands are not producing enough hormone. This is a hallmark of primary adrenal insufficiency (Addison’s disease) or secondary adrenal insufficiency (due to pituitary or hypothalamic dysfunction).

Common Causes of Low Cortisol

• Addison’s disease – autoimmune destruction of the adrenal glands
• Pituitary tumour or damage – reduces ACTH, impairing cortisol release
• Long-term corticosteroid use – suppresses the HPA axis, leading to withdrawal insufficiency
• Congenital adrenal hyperplasia – enzyme deficiencies

Symptoms of low cortisol include fatigue, weight loss, low blood pressure, hyperpigmentation (in Addison’s), and salt cravings. If you’re experiencing these, a morning cortisol test is a good starting point.

Cortisol During Pregnancy

Pregnancy naturally raises cortisol levels, especially in the third trimester, due to the placenta producing CRH and oestrogen increasing corticosteroid-binding globulin. Morning cortisol can be 2–3 times the normal non‑pregnant level. This is physiological and not a sign of disease. However, if a pregnant woman has symptoms of Cushing’s (e.g., rapid weight gain, striae, hypertension), further testing with a 24‑hour urine cortisol or dexamethasone suppression test is warranted.

How to Prepare for a Morning Cortisol Test

Timing is everything. The test should be drawn between 7:00 and 9:00 a.m. after you’ve been awake for at least 30 minutes but before breakfast. Avoid intense exercise, alcohol, and caffeine for 24 hours before the test. Let your doctor know about any medications, especially birth control pills, corticosteroids, or antidepressants. Also, stress the night before can raise cortisol, so try to get a good night’s sleep.

Medications That Affect Cortisol Levels

Several medications can interfere with the test or alter your natural cortisol production. Common ones include:

• Oestrogen-containing contraceptives – increase cortisol binding proteins, raising total cortisol
• Corticosteroids (prednisone, hydrocortisone) – can suppress endogenous cortisol
• Anticonvulsants (phenytoin, carbamazepine) – increase cortisol metabolism
• Rifampin – accelerates cortisol clearance
• Lithium – may increase cortisol

Always inform your lab and doctor of any medications or supplements you take.

Cortisol and Sleep Cycles

Your circadian rhythm is the most important factor. Shift workers, those with jet lag, or people with insomnia often have blunted or shifted cortisol peaks. This can make a single morning cortisol test less reliable. In such cases, we may use a series of timed samples or a 24‑hour urine cortisol.

Other Tests for Adrenal Function

Morning cortisol alone is not diagnostic. If levels are borderline, your doctor may order:

• DST (Dexamethasone Suppression Test) – to confirm Cushing’s syndrome
• ACTH stimulation test – to assess adrenal reserve
• 24‑hour urinary free cortisol – overall daily cortisol production
• CRH stimulation test – to differentiate pituitary vs. ectopic ACTH sources
• Imaging – CT or MRI of pituitary/adrenals

Don’t panic if your morning cortisol is slightly out of range. Many factors transiently affect it. Your doctor will repeat the test and correlate with your symptoms before making a diagnosis.