Cortisol is the main stress hormone, peaking at dawn to wake you and falling to a whisper at midnight. Both the chronic excess of Cushing syndrome and the failure of adrenal insufficiency are medical emergencies in slow motion.
Standard range versus optimal range
| Framework | Cortisol value | Source |
|---|---|---|
| Typical morning, 8 am | about 6-18 µg/dL | Endocrine Society context |
| After 1 mg dexamethasone, normal | below 1.8 µg/dL | Endocrine Society 2008 |
| Midnight, healthy | near zero, rhythm trough | Endocrine Society context |
When it runs high
A high cortisol can be stress, poor sleep, alcohol, depression or medication, which is why guidelines insist on dynamic tests rather than single values to diagnose true Cushing syndrome, the rare cortisol-producing disease.
- Stress, pain and acute illness, physiological
- Glucocorticoid medications, the commonest cause overall
- Depression, alcohol dependence and severe obesity, pseudo-Cushing states
- Cushing syndrome from pituitary, adrenal or ectopic tumors, rare
- Pregnancy raising binding protein
When it runs low
Low morning cortisol, especially with fatigue, weight loss, salt craving and low blood pressure, demands testing for adrenal insufficiency. Stopping long-term steroid tablets suddenly is the classic preventable cause.
- Adrenal insufficiency, Addison disease
- Pituitary failure cutting ACTH supply
- Abrupt withdrawal of steroid medication
- Critical illness exhaustion of the axis
The hormone with a daily curve
Cortisol surges within thirty minutes of waking, the cortisol awakening response, then declines through the day to near zero at midnight. This rhythm is so fundamental that a single random blood cortisol is almost uninterpretable, which is why the Endocrine Society explicitly recommends against random values and instead uses tests of the rhythm itself, late-night salivary cortisol, 24-hour urine free cortisol, and the dexamethasone suppression test.
When the axis breaks in either direction
Cushing syndrome turns the volume up permanently, producing the recognizable pattern of central weight gain, purple stretch marks, easy bruising, muscle weakness and high blood pressure, a diagnosis built from two abnormal rhythm tests, never one blood draw. The opposite failure, adrenal insufficiency, is subtler and more dangerous, fatigue and dizziness progressing to a crisis under stress, and it is diagnosed by measuring how cortisol responds to an ACTH injection.
The everyday meaning
Outside these rare diseases, cortisol is the chemistry of lifestyle, chronically elevated by short sleep, unresolved stress and excess alcohol, and flattened into an unhealthy rhythm by night-shift work. Salivary four-point day curves, popular in functional medicine, lack guideline backing for diagnosis, but the underlying principle is solid, protect sleep and the cortisol curve largely protects itself.
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Related biomarkers DHEA-S · TSH