Cortisol

How cortisol is controlled

Your pituitary gland releases a messenger called ACTH that tells the adrenal glands how much cortisol to make. When cortisol is high enough, it signals the brain and pituitary to ease off. This loop keeps levels within a working range.

Cortisol also follows a daily rhythm. It's normally highest in the early morning, helping you wake and mobilize energy, and lowest late at night. That rhythm is why the time of a cortisol test matters so much.

Ways to measure it

Cortisol can be measured several ways, and each answers a slightly different question:

• Blood: often drawn in the morning, sometimes with a second sample in the afternoon.
• Urine: a 24-hour collection shows the total amount released over a full day.
• Saliva: a late-night sample checks whether cortisol drops as it should before sleep, and can be collected at home.
• Suppression and stimulation tests: a dose of dexamethasone or a synthetic ACTH is given to see whether cortisol responds normally.

What abnormal results can mean

Persistently high cortisol is called Cushing's syndrome. The most common cause is long-term use of glucocorticoid medicines such as prednisone. Less often, a tumor in the pituitary, adrenal gland or elsewhere drives excess production. Signs can include weight gain around the face and upper back, thin arms and legs, easy bruising, purple stretch marks and high blood sugar. Diagnosis usually requires two different abnormal tests.

Low cortisol points to adrenal insufficiency, either from damage to the adrenal glands (Addison disease) or from a pituitary problem. It can cause fatigue, weight loss, low blood pressure and, in a crisis, can be life-threatening.

Cortisol, stress and 'adrenal fatigue'

Everyday stress, poor sleep, illness, intense exercise, pregnancy and some medicines, including birth control pills, can all shift a cortisol result. That makes a single reading easy to over-interpret. 'Adrenal fatigue' is not a recognized diagnosis, and a cortisol test on its own can't explain why you feel tired.

If a result is abnormal, follow-up testing is usually needed to confirm it and find the cause. Some functional panels, such as dried urine tests, map the daily cortisol curve; they can be informative, but they don't replace the standard tests used to diagnose adrenal disease.

If you're dealing with long-term stress and poor sleep, the most useful steps are usually practical ones: protecting sleep time, regular physical activity, limiting alcohol and getting help for anxiety or depression. A clinician can decide whether any cortisol testing would actually change your care.