Low cortisol: what it means, causes and how it is tested

Low cortisol means the body isn’t making enough of the hormone, or that a blood result came back under a lab’s range. The first is a medical condition called adrenal insufficiency, and Addison’s disease is one form of it. The second is a lab finding that needs context before it means anything.

Get emergency care now if you have any of these.

• Vomiting you can’t stop, or severe diarrhea, together with severe weakness.
• Fainting, or dizziness on standing that doesn’t settle.
• Weakness so severe you can’t do your usual daily activities.
• You take a corticosteroid (steroid) medicine and can’t keep it down, or you have a severe infection.

These signs come from NIDDK’s advice for people taking steroid medicine (severe infection, severe diarrhea, or vomiting that stops you keeping pills down) and from a 2013 paper’s description of an imminent adrenal crisis (nausea and vomiting, a large drop in blood pressure, weakness that stops daily activities). Many other illnesses cause them too, and they need urgent care either way.

Call 911 or go to the nearest emergency room. Don’t wait for a test or an appointment. Suspected adrenal crisis is treated without waiting for test results. If you have a known adrenal condition, follow the emergency plan your prescriber gave you. See adrenal crisis for more.

The rest of this page is for the far more common situation: you have symptoms, or a result, and want to know what it means and what to do next.

Cortisol AM and PM

A morning result and a later one, because cortisol changes through the day. Follow the times on your lab order.

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Not for emergencies. If you have repeated vomiting, severe weakness or fainting, get urgent care instead of ordering a test. If you take a steroid medicine, ask your prescriber how it affects results.

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What low cortisol means

Cortisol is made by the adrenal glands, which sit above the kidneys. MedlinePlus says it affects almost every organ and tissue. It helps with your response to stress, inflammation, blood sugar, metabolism and blood pressure.

Your brain controls the supply in a chain. The hypothalamus signals the pituitary gland, the pituitary releases ACTH, and ACTH tells the adrenal glands to make cortisol. A problem at any of the three steps can leave you short.

The word “low” also needs a time attached. Cortisol rises to a peak in the early morning and reaches its lowest point early in sleep.

A level that is ordinary at 11 p.m. can be a concern at 8 a.m. A published range for serum cortisol shows the same drop. One review gives 3 to 23 µg/dL for total serum cortisol at 8 a.m. and 3 to 13 µg/dL at 4 p.m. Labs use different methods and print their own ranges, so use the one on your report. The normal range page has more, and the cortisol units converter helps if your report is in nmol/L. A result under your lab’s range is something to go over with a clinician. It is not a diagnosis.

Doctors describe three levels of adrenal insufficiency, according to NIDDK:

• Primary (Addison’s disease): the adrenal glands themselves are damaged.
• Secondary: the pituitary doesn’t make enough ACTH.
• Tertiary: the hypothalamus makes less of the hormone that drives the pituitary.

Possible causes

NIDDK lists these causes by level.

Level	Causes NIDDK names
Adrenal glands (primary)	Autoimmune disease, which is the usual cause in developed countries. Tuberculosis. Infections linked to HIV/AIDS. Cancer in the adrenal glands. Surgical removal of the glands. Bleeding into them. Genetic disorders. Some medicines, including certain antifungals and the anesthetic etomidate.
Pituitary (secondary)	Autoimmune disease. Pituitary tumors or infection. Bleeding in the pituitary. Genetic disorders. Pituitary surgery. Traumatic brain injury.
Hypothalamus (tertiary)	Stopping long-term corticosteroids. Recovery from Cushing’s syndrome, after which the adrenal glands may be slow to recover.

NIDDK says the most common cause overall is suddenly stopping corticosteroids that were taken for a long time. That is why you should never stop a steroid medicine on your own. Your doctor tapers the dose over weeks or months and watches for symptoms, because recovery can take many months. If you have taken a steroid for a long time and want to come off it, talk to the prescriber first.

Not every low reading comes from one of these conditions. Total cortisol depends partly on carrier proteins in blood. Nephrotic syndrome, a kidney condition, can lower total cortisol. In critically ill people with low albumin, one study found lower total cortisol but similar free cortisol (Endocrine Reviews, 2024). This is one reason doctors don’t act on a single number. More on this on the causes of low cortisol page.

What it can feel like

The most common symptoms of adrenal insufficiency, per NIDDK, are long-lasting fatigue, muscle weakness, loss of appetite, weight loss and abdominal pain. Others it lists:

• Nausea, vomiting or diarrhea
• Low blood pressure that is worse on standing, with dizziness or fainting
• Irritability and depression
• Joint pain
• Salt cravings
• Low blood sugar
• Irregular or absent periods
• Less interest in sex

Addison’s disease can also darken the skin, most noticeably on scars, skin folds, pressure points, the lips and the inside of the cheek.

These symptoms usually build slowly. NIDDK says they can be missed or mistaken for other illnesses, and that sometimes they first show up during an adrenal crisis. In one small single-center study of 60 people with primary adrenal insufficiency in Poland, the average time from first symptoms to diagnosis was about 6 months for people diagnosed without a crisis and about 9 months for those diagnosed in or near one, and 26 of the 60 were first diagnosed during or just before an adrenal crisis (Int J Endocrinol, 2013). That is the case for taking persistent symptoms to a clinician rather than waiting. It is not a reason to assume your own tiredness is adrenal. See low cortisol symptoms and low cortisol in women and men.

What about “adrenal fatigue”?

Adrenal fatigue is not a recognized medical diagnosis. A 2024 paper in the Journal of the Endocrine Society says it has never been scientifically proven to exist. It says the online symptom scores and salivary cortisol profiles sold for it have never been validated, and that the accepted tests are usually normal in people given the label. It also warns that some “adrenal extract” products contain steroid hormones, which could cause adrenal insufficiency. Adrenal insufficiency itself is a real condition with a defined work-up. See adrenal fatigue.

When to see a clinician

Book an appointment soon, not an emergency visit, if you have:

• Fatigue or weakness that has lasted and has no clear reason.
• Weight loss or loss of appetite you can’t explain.
• Dizziness when you stand, or darkening patches of skin.
• A history that raises the odds. NIDDK lists long-term steroid medicine, pituitary surgery, traumatic brain injury, HIV/AIDS and autoimmune disease among the causes and risk groups.

NIDDK’s advice is plain: if you always feel tired, weak or are losing weight, ask your health care professional whether you might have adrenal insufficiency. It adds that early treatment can help prevent an adrenal crisis.

If you take a steroid medicine and get sick, tell your prescriber early. NIDDK says people with adrenal insufficiency need higher doses during illness, surgery and injury, and the prescriber decides how.

How low cortisol is tested

Testing is done in steps, and a clinician usually directs them.

1. History and symptoms. NIDDK says suspicion usually starts here, and that early on, adrenal insufficiency can be hard to diagnose because symptoms come on slowly.
2. Blood cortisol, usually in the morning, often with ACTH. The two are measured together to help find which gland is involved, according to MedlinePlus. A review of diagnosis describes paired measurement of serum cortisol and plasma ACTH as the next step once primary adrenal insufficiency is suspected. Morning draws are used because cortisol is highest then.
3. A stimulation test, when the result isn’t clear. In the most common version, you get an injection of synthetic ACTH, and blood is drawn before and 30 or 60 minutes after. A normal response is a rise in cortisol. People with Addison’s disease show little or no rise, NIDDK says.
4. Other tests to find the cause. NIDDK lists antibody tests for autoimmune Addison’s disease, CT scans of the abdomen, and MRI of the pituitary. Two more dynamic tests, an insulin tolerance test and a CRH stimulation test, are used when ACTH results are unclear or a pituitary problem is suspected. The insulin tolerance test needs a health professional present throughout.

A cortisol blood test is one early step in this list. For the full range of cortisol tests and what each answers, see the cortisol test guide. For the ACTH step, see the ACTH blood test. For how these fit together for low cortisol, see testing for low cortisol.

Why one result doesn’t settle it

A single blood cortisol can’t diagnose adrenal insufficiency, and it can’t rule it out. Here is why.

• Time of day. The same body gives different values at 8 a.m. and 4 p.m.
• Everyday factors. MedlinePlus lists stress, exercise, pregnancy, temperature extremes, steroid use or stopping it suddenly, and some medicines, such as birth control pills, as reasons for abnormal results that are not a disease.
• The lab method. In one study, five automated immunoassays read 1.08 to 1.36 times higher than a mass spectrometry reference. In another analysis of a stimulation-test cut-off, the share of people misclassified ranged from 4% to 19% depending on which of four assays was used, at a cut-off of 500 nmol/L. A 2026 study says its morning-cortisol cut-offs are valid only for the assay it used.
• Carrier proteins. Oral estrogen raises them, and so raises total cortisol. Some illnesses lower them.
• Medicines. Steroid medicines can change results, and some lab methods can read them as cortisol.
• In-between values. When a morning result is neither clearly low nor clearly sufficient, a stimulation test is recommended, according to a study of pituitary-related adrenal insufficiency (J Endocrinol Invest, 2026).
• No cause. MedlinePlus says a cortisol test alone can’t identify the cause of an abnormal level, so further testing is usually needed.

The practical result is that doctors repeat, pair or stimulate rather than act on one number. You should expect the same from your own result.

If you are thinking about ordering a test

A morning cortisol with a later sample is a reasonable way to get a number to bring to a clinician, if you have no emergency signs. For a low-cortisol question the morning value carries the most weight. The later sample shows how far the level falls during the day.

A few limits apply:

• It is a first look, not a work-up. A result that is unusual will need ACTH or a stimulation test, which a clinician arranges.
• The seller’s page for its morning-and-later test is unclear about when the second sample is taken and doesn’t say whether it is one visit or two. Check this before you order, and follow the timing on your lab order. The page states no fasting rule either, so follow the instructions on your order. Our page on AM and PM timing covers the practical side.
• If you take a steroid medicine, tell your prescriber before you test, and don’t stop or change the medicine for the test.
• Tiredness on its own has many possible causes. Tests for tiredness explains what else to consider first.

Questions people ask

Is low cortisol good or bad?

Low cortisol isn’t a goal. The body needs cortisol, and MedlinePlus says untreated Addison disease can be fatal. The exception is the daily dip: late evening and night are meant to be low. What matters is a level that is low for the time of day, along with symptoms, and that is a question for a clinician.

What does a low morning cortisol mean?

On its own, it means more testing. A low morning value can point toward adrenal insufficiency, but a clinician looks at it alongside ACTH, your symptoms, your medicines and the lab’s method. Many other things can lower or alter a single reading, as the section above explains.

What is an AM cortisol?

It is a blood cortisol drawn in the morning, when levels are normally highest. MedlinePlus says morning samples are paired with one around 4 p.m. when two are taken. Doctors use the morning level in suspected adrenal insufficiency, and the AM and PM page explains the timing.

How is high cortisol different from low?

They have different symptoms and different tests. MedlinePlus lists weight gain, thin arms and legs, a rounded face, easy bruising and wide purple stretch marks for too much cortisol, and long-lasting fatigue, muscle weakness, loss of appetite, weight loss and abdominal pain for too little. See high cortisol.

Keep reading

• Low cortisol symptoms

  What each symptom can mean, and what doesn't point to cortisol.

• Causes of low cortisol

  Adrenal, pituitary and medicine-related causes.

• Adrenal crisis

  The emergency signs and what to do.

• Low cortisol in women and men

  How it can differ and what to ask.

• Cortisol test guide

  Which cortisol test answers which question.

• ACTH blood test

  The hormone that signals the adrenal glands.