What is cortisol?
Cortisol is a hormone made by the adrenal glands, two small glands above the kidneys. It affects almost every organ: it helps your body respond to stress (hence the "stress hormone" nickname), reduces inflammation and helps control blood sugar and blood pressure. The pituitary gland controls it through a hormone called ACTH.
Cortisol follows a daily rhythm. It is highest in the morning and falls through the day, which is why the time of your test matters so much. A cortisol test is used to help diagnose or rule out conditions with too much cortisol (Cushing's syndrome) or too little (Addison disease and other forms of adrenal insufficiency).
Cortisol levels by time of day
| Time of blood draw | mcg/dL (µg/dL) | nmol/L | Source |
|---|---|---|---|
| 8 a.m. | 5 to 25 | 138 to 690 | MedlinePlus |
| 6 to 10 a.m. | 6.0 to 18.4 | 166 to 508 | ARUP |
| 4 to 8 p.m. | 2.7 to 10.5 | 75 to 290 | ARUP |
To convert mcg/dL to nmol/L, multiply by 27.6 (the ARUP nmol/L figures are our conversions). The same afternoon number that is normal at 6 p.m. would be low at 8 a.m., so always note when you collected.
MedlinePlus and ARUP Laboratories reference intervals.
What high cortisol means
MedlinePlus says the most common cause of abnormal cortisol is taking steroid medicines for a long time, or stopping them suddenly. Other causes of high cortisol include:
- Cushing's syndrome from a pituitary tumor making too much ACTH, a tumor elsewhere (for example in the lungs) making ACTH, or an adrenal tumor making cortisol
- Stress, acute illness, pregnancy, exercise and hot or cold temperatures
- Birth control pills and other estrogens
High cortisol can also come and go with depression, anxiety, alcohol use disorder, poorly controlled diabetes and obesity. MedlinePlus calls this pseudo-Cushing's syndrome, or non-neoplastic hypercortisolism.
The Endocrine Society's guideline recommends starting with a test that has high diagnostic accuracy: a 24-hour urine cortisol, a late-night saliva cortisol, or an overnight dexamethasone suppression test. If a morning cortisol is high and you have symptoms such as a round face, thin arms and legs, easy bruising or wide purple stretch marks, ask your doctor about those tests.
What low cortisol means
Low cortisol may mean Addison disease, where the adrenal glands do not make enough cortisol (common causes include autoimmune disease and infections such as tuberculosis), or secondary adrenal insufficiency, where the pituitary does not signal the adrenals properly. Steroid medicines, including pills, skin creams, eye drops, inhalers and joint injections, can also suppress the body's own cortisol.
Symptoms include long-lasting fatigue, muscle weakness, loss of appetite, weight loss and belly pain. Low cortisol can be serious. The Endocrine Society recommends a short corticotropin (ACTH) stimulation test to confirm the diagnosis, or morning ACTH and cortisol as an initial screen. ARUP's normal response is a peak above 18.0 mcg/dL after the stimulation dose. If your morning cortisol is low and you feel unwell, see a doctor promptly.
Worked example: a cortisol of 6.5 drawn at noon
Say a 41-year-old man does his home collection at noon and gets a cortisol of 6.5 mcg/dL. Against MedlinePlus's 8 a.m. range (5 to 25 mcg/dL) it sits near the bottom; against ARUP's 4 to 8 p.m. range (2.7 to 10.5 mcg/dL) it would be mid-range. Noon falls between the two windows, so the number cannot be judged well.
He also uses a steroid inhaler for asthma, and inhaled steroids are on the list of medicines that can suppress the body's own cortisol. The sensible first step, if he feels well, is a repeat at 8 a.m. If he has long-lasting fatigue, weakness, weight loss or belly pain, he should see a doctor promptly instead.
Questions for the doctor: Should I repeat it at 8 a.m.? Could my inhaler be lowering it? If a morning value is low, do I need morning ACTH or a short ACTH stimulation test, as the Endocrine Society recommends?
What can change cortisol
- Time of day, the biggest factor.
- Steroid medicines in any form, and starting or stopping them. Never stop a steroid suddenly without medical advice.
- Estrogen, birth control pills, androgens and anti-seizure medicines (MedlinePlus).
- Vigorous exercise the day before, acute stress, illness and pregnancy.
- Depression, anxiety, heavy drinking, poorly controlled diabetes and obesity, which can drive pseudo-Cushing's.
How to test cortisol
- Test early in the morning, as MedlinePlus advises, and at the same time every time you retest.
- Avoid vigorous exercise the day before.
- List every steroid you use, including creams, inhalers and eye drops.
- For suspected Cushing's, your doctor will use urine, late-night saliva or dexamethasone tests instead of a single morning blood level.
Common questions about cortisol
Why do some doctors test cortisol twice in one day?
MedlinePlus says blood is often drawn in the morning, when cortisol is normally highest, and again around 4 p.m., when it is much lower. The pair shows whether the normal daily fall is there, which one sample cannot.
Blood, urine or saliva?
MedlinePlus says urine and saliva cortisol are also accurate ways to estimate blood levels. A 24-hour urine collection captures the whole day's output, and late-night saliva is one of the Endocrine Society's first tests for Cushing's. Stress and exercise raise cortisol, so you may be asked to rest before a blood test, and before a saliva test you may need to stop certain medicines, including skin creams.
What is tested with cortisol?
MedlinePlus says a cortisol test alone cannot diagnose the cause of an abnormal level, so more tests usually follow, such as ACTH. DHEA-S is the other adrenal hormone on most panels, and glucose is worth a look because cortisol helps control blood sugar.
Which at-home tests include cortisol
Cortisol is the one hormone on every SiPhox Health panel: Longevity Essentials, Heart & Metabolic, Thyroid Focus, Hormone Focus, Ultimate 360 and GLP Optimization (which labels it morning cortisol). Longevity Essentials and Hormone Focus add the cortisol:DHEA-S ratio alongside DHEA-S, and Longevity adds a testosterone:cortisol ratio; we found no clinical guideline that uses either ratio.
Because your result depends on timing, do your EasyDraw collection in the morning and at a similar time each cycle. SiPhox also sells a separate Advanced Stress & Sleep Cortisol Test that uses four saliva samples through the day ($120 on 29 September 2026), which shows your daily curve rather than one point. Neither replaces the tests a doctor uses to diagnose Cushing's or Addison disease. See our SiPhox review and longevity blood test guide.
A note on home samples: SiPhox's partner lab tests capillary blood collected from the upper arm. SiPhox says its results show a 95% to 99% correlation with venous draws in its own quarterly comparisons against Labcorp and Quest, but it has not published a study of the EasyDraw device. If a result would change a treatment decision, confirm it with a venous test through your doctor.
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The default panel: heart, metabolic, hormone and inflammation markers in one draw.
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Hormone Focus
Sex hormones for men and women, including PSA for men and progesterone for women.
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Heart & Metabolic
Lipids plus kidney and liver function: the panel for cardiovascular and metabolic risk.
Check priceFrequently asked questions
What is a normal cortisol level in the morning?
About 5 to 25 mcg/dL (138 to 690 nmol/L) at 8 a.m. according to MedlinePlus, or 6.0 to 18.4 mcg/dL between 6 and 10 a.m. at ARUP.
What is a normal cortisol level in the afternoon?
Lower. ARUP uses 2.7 to 10.5 mcg/dL for blood drawn between 4 and 8 p.m.
What causes high cortisol?
Most often long-term steroid medicines. Other causes include stress, illness, pregnancy, birth control pills, pseudo-Cushing's (depression, alcohol use disorder, obesity) and, rarely, Cushing's syndrome from a pituitary or adrenal tumor.
Can a blood test diagnose Cushing's syndrome?
Not a single morning blood cortisol. The Endocrine Society recommends 24-hour urine cortisol, late-night saliva cortisol or a dexamethasone suppression test as first tests.
Is cortisol higher in men or women?
MedlinePlus and ARUP use the same cortisol range for men and women. Timing, medicines and pregnancy matter far more than sex.
Sources
- MedlinePlus Medical Encyclopedia: Cortisol blood test
- MedlinePlus Lab Tests: Cortisol test
- ARUP Laboratories Test Directory: Cortisol, serum
- Nieman LK et al. The diagnosis of Cushing's syndrome: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab 2008
- Bornstein SR et al. Diagnosis and treatment of primary adrenal insufficiency: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab 2016
- SiPhox Health: panel comparison (checked 29 Sep 2026)
- SiPhox Health: Longevity Essentials panel
- SiPhox Health: Advanced Stress & Sleep Cortisol Test