Low cortisol levels in blood usually come from adrenal gland damage, pituitary disease, long steroid use, or rare genetic problems.
When a blood test shows low cortisol, it can feel worrying straight away. Cortisol helps control blood pressure, blood sugar, salt balance, and the way the body handles stress. So low levels can leave you tired, dizzy, and unwell, and in rare cases can lead to a medical emergency.
This article explains the main causes of low cortisol, how doctors group those causes, and which symptoms and test results deserve quick follow-up. It is general information only. It cannot replace advice from a doctor who knows your health history and can review your full set of test results.
What Low Cortisol In Blood Means
Cortisol is a steroid hormone made by the adrenal glands, two small glands that sit just above each kidney. The brain controls cortisol production through the hypothalamus and the pituitary gland, which release signals that tell the adrenals when to make more or less hormone.
When a lab report shows low cortisol at the wrong time of day, doctors think about a problem anywhere along this chain. Low levels can come from damaged adrenal glands, a pituitary or hypothalamus problem, or outside medicines that “switch off” natural hormone signals. Together, these problems sit under the heading “adrenal insufficiency”.
Some people have mild low readings without clear symptoms, while others have very low levels and feel unwell for months. Very low cortisol during illness, surgery, or injury can lead to an adrenal crisis, which needs urgent treatment in hospital.
Main Causes Of Low Cortisol Levels In Blood
Doctors sort the causes of low cortisol levels in blood into three broad groups: problems in the adrenal glands themselves (primary adrenal insufficiency), problems in the pituitary or hypothalamus (secondary or tertiary adrenal insufficiency), and causes linked to medicines or severe illness.
| Cause Category | Main Problem Area | Typical Examples Or Triggers |
|---|---|---|
| Autoimmune Addison’s Disease | Immune attack on adrenal glands | Immune system destroys adrenal cortex over time, often with other autoimmune conditions |
| Infections Affecting Adrenals | Adrenal tissue damage | Tuberculosis, fungal infections, HIV-related infections, long-standing sepsis |
| Genetic Or Congenital Conditions | Abnormal adrenal development or enzymes | Congenital adrenal hyperplasia, adrenal hypoplasia, rare enzyme defects |
| Bleeding, Injury, Or Surgery | Sudden adrenal gland damage | Bilateral adrenal hemorrhage, clotting problems, major abdominal surgery |
| Pituitary Or Hypothalamus Disease | Low ACTH or CRH signals | Pituitary tumours, surgery, radiotherapy, head injury, infiltrative diseases |
| Long-Term Steroid Use | Suppressed hypothalamus–pituitary–adrenal axis | Chronic tablets, injections, inhalers, or strong creams stopped or tapered too quickly |
| Other Medicines | Reduced cortisol production or faster breakdown | Some antifungals, epilepsy medicines, immune-suppressing drugs, cancer treatments |
| Severe Illness Or Critical Care | Stress-related adrenal dysfunction | Sepsis, major trauma, cardiac surgery, long stay in intensive care |
| Lab Or Sampling Issues | Collection or timing problem | Blood drawn late in the day, wrong tubes, steroid dose taken before the test |
Primary Adrenal Insufficiency
Primary adrenal insufficiency means the adrenal glands themselves cannot make enough cortisol. The most common cause in many countries is autoimmune Addison’s disease, where the immune system slowly damages the adrenal cortex and may also affect other organs . Other causes include infections such as tuberculosis, bleeding into the glands, and spread of cancer.
People with primary adrenal insufficiency often have low cortisol, low aldosterone, and high ACTH. Skin darkening, salt craving, low blood pressure, and weight loss are common patterns. Blood tests and an ACTH stimulation test help confirm this group of causes.
Secondary And Tertiary Adrenal Insufficiency
In secondary adrenal insufficiency, the pituitary gland does not make enough ACTH, so healthy adrenal glands receive a weak signal and produce too little cortisol. In tertiary adrenal insufficiency, the hypothalamus sends too little CRH, which again reduces ACTH release and cortisol output .
These forms often follow pituitary tumours, brain surgery, radiotherapy, or long periods of glucocorticoid treatment. Typical features include low cortisol with low or in-range ACTH, pale skin rather than tanning, and fewer salt balance problems because aldosterone may remain normal.
Medicines And Long-Term Steroid Treatment
Long-term use of steroid tablets, injections, inhalers, or strong creams is one of the most common causes of low cortisol levels in blood. The body senses the extra steroid and “turns down” its own production. If those medicines stop suddenly or are reduced too quickly, the adrenal glands may not keep up, and cortisol drops .
Other medicines can also affect cortisol. Some antifungal drugs slow down cortisol production. Certain epilepsy and HIV medicines speed up cortisol breakdown in the liver. Cancer treatments and immune-suppressing medicines may damage the adrenal glands or the pituitary region. Because drug lists change over time, your doctor or pharmacist is the best person to review your exact prescription list.
Short-Term Factors And Lab Pitfalls
Cortisol follows a daily rhythm, highest in the early morning and lower later in the day. A sample taken late morning or afternoon can look low without any real disease. Severe illness, surgery, or pregnancy can also shift binding proteins in the blood and alter measured values. That is why doctors often repeat tests, or use stimulation tests, before saying that low cortisol is persistent.
Even something as simple as taking a steroid tablet before the test, or using a strong steroid cream on a wide area of skin, can change the result. When you book repeat tests, give the lab and your doctor a full list of medicines, creams, and inhalers so the result can be read in the right context.
Low Cortisol Levels In Blood Causes And Risk Patterns
Some patterns in age, sex, and medical history raise the chance that a low cortisol reading reflects true adrenal insufficiency. For example, autoimmune Addison’s disease is more common in adults between 30 and 50 years old and affects women slightly more often than men . It also clusters with other autoimmune conditions such as type 1 diabetes or thyroid disease.
Long-term steroid use is a frequent background factor in older adults and people with asthma, rheumatoid arthritis, inflammatory bowel disease, or certain cancers. Anyone who has used moderate or high steroid doses for months, then stops without a careful taper, sits in a higher risk group for adrenal insufficiency.
A history of pituitary tumours, surgery to the brain, or radiotherapy to the head tilts the balance toward secondary adrenal insufficiency. People with these histories often need regular hormone checks, including cortisol and ACTH, especially if they report fatigue, dizziness, or drops in blood pressure.
Symptoms Linked To Low Cortisol In Daily Life
Symptoms can build slowly and may look vague at first. Many people blame them on stress or aging. Still, certain clusters make doctors think about causes of low cortisol levels in blood rather than simple tiredness.
Common Day-To-Day Symptoms
- Ongoing fatigue that does not lift with rest
- Loss of appetite and unplanned weight loss
- Muscle weakness, especially in the legs
- Dizziness or faint feelings when standing
- Salt craving or a strong taste for salty foods
- Stomach pain, nausea, or bouts of vomiting
- Low mood, irritability, or poor concentration
In primary adrenal insufficiency, blood pressure often runs low, and the skin and gums may darken. People can notice new patches of darker skin around scars, knuckles, or skin folds. In secondary adrenal insufficiency, skin colour may stay unchanged, but low energy and low blood pressure remain common.
Patterns That Should Raise Concern
Low cortisol becomes more worrying when symptoms cluster or change quickly. Red flags include a sharp drop in weight, new nausea or vomiting, repeated fainting, and flu-like episodes that linger. People with type 1 diabetes who suddenly need less insulin and have frequent low blood sugar episodes deserve extra care, because this pattern can appear with Addison’s disease.
If these changes appear on top of a known risk factor, such as long-term steroid treatment or known pituitary disease, doctors usually bring cortisol testing forward rather than waiting for a routine check. A clear story and set of symptoms often guide which tests to order first.
Testing For Low Cortisol Levels
Testing starts with timing. Most doctors ask for an early morning blood sample, usually between 7 and 9 a.m., when cortisol should sit at its daily peak. A single low morning reading does not prove adrenal insufficiency on its own, but a very low result makes this diagnosis more likely .
First-Line Blood Tests
Early tests often include:
- Morning serum cortisol
- ACTH level to see if hormone signals from the pituitary are low or high
- Basic electrolytes (sodium and potassium), glucose, and kidney function
- Sometimes renin and aldosterone, especially in suspected primary adrenal insufficiency
Values from these tests guide the next steps. A low cortisol with raised ACTH points to primary adrenal insufficiency. A low cortisol with low or normal ACTH leans toward secondary or tertiary causes.
Dynamic Tests And Imaging
When the picture remains unclear, doctors may use stimulation tests to see how the adrenal glands respond. The most used test is the ACTH stimulation test, where a synthetic form of ACTH is injected and cortisol is measured before and after the injection. A weak rise in cortisol suggests adrenal insufficiency.
| Test Or Assessment | What It Checks | When It Is Considered |
|---|---|---|
| Morning Serum Cortisol | Baseline cortisol at daily peak | First-line test in most people with symptoms |
| ACTH Level | Signal from pituitary to adrenal glands | Distinguishes primary from secondary or tertiary causes |
| ACTH Stimulation Test | Adrenal response to strong ACTH signal | Confirms adrenal insufficiency when baseline levels sit in a grey zone |
| Insulin Tolerance Or Metyrapone Tests | Broader check of hypothalamus–pituitary–adrenal axis | Specialist settings when diagnosis remains uncertain |
| Pituitary MRI | Structure of pituitary and nearby brain regions | Suspected pituitary or hypothalamus disease |
| Adrenal CT Or MRI | Structure of the adrenal glands | Suspected tumour, infection, bleeding, or enlargement |
Guidance on the work-up of adrenal insufficiency is available from major endocrine groups, including detailed patient information from the
U.S. NIDDK adrenal insufficiency overview
and practical explanations from the
Endocrine Society adrenal insufficiency page.
When Low Cortisol Levels Become An Emergency
Adrenal crisis is a sudden, severe form of adrenal insufficiency. It can happen when someone with low cortisol faces an illness, accident, or surgery and the body cannot raise cortisol to match the stress. Blood pressure drops, blood sugar may fall, and people can lose consciousness if treatment is delayed .
Warning signs include severe weakness, vomiting, stomach or lower back pain, confusion, and very low blood pressure. People with known adrenal insufficiency usually carry a steroid card or emergency injection plan and are told to seek urgent care if these symptoms start. Anyone with low cortisol and sudden severe illness should receive fast medical review in an emergency department.
Talking With Your Doctor About Low Cortisol Results
If your lab report shows low cortisol, the next step is a clear conversation with a doctor or endocrinologist. Take a full list of medicines, including steroid tablets, inhalers, nasal sprays, and creams. Share any history of pituitary, brain, or adrenal problems. This gives the doctor a strong base to judge which causes of low cortisol levels in blood fit your story.
Ask which group your doctor thinks you fall into: primary adrenal insufficiency, a pituitary or hypothalamus problem, medicine-related suppression, or a short-term effect of illness. Check whether you need repeat blood tests, an ACTH stimulation test, or imaging. If adrenal insufficiency is confirmed, ask for written sick-day rules and an emergency plan so that you and your family know what to do during illness or surgery.
Low cortisol is not a problem to ignore, but many causes can be managed well once they are found. Careful testing, clear communication with your medical team, and prompt action during illness help lower the risk of adrenal crisis and improve day-to-day wellbeing.