◇Emerging Research

Is Cortisol Testing Worth It?

Why single cortisol tests are rarely useful, the "adrenal fatigue" myth debunked, and when specialised testing actually matters

Published 23 January 2026 · 11 min read

Studies examined in a systematic review found NO scientific basis for "adrenal fatigue"

Source: [1]

The Short Answer

Skip the random cortisol test. "Adrenal fatigue" does not exist. Random cortisol blood tests have very limited clinical utility due to the hormone's dramatic circadian variation. The Endocrine Society is clear: there is "no scientific proof" for adrenal fatigue. A systematic review of 58 studies concluded adrenal fatigue "is still a myth."^[1][2] Real adrenal disorders (Addison's disease, Cushing's syndrome) are rare and require specialised dynamic testing—not a single morning blood draw. If you're experiencing fatigue, investigate thyroid function, iron levels, and sleep quality first.

What Cortisol Actually Does

Cortisol is a steroid hormone produced by your adrenal glands—small organs sitting atop your kidneys. While often called the "stress hormone," this label dramatically undersells cortisol's importance. It's essential for life.

Your hypothalamus, pituitary gland, and adrenal glands work together in what's called the HPA axis (hypothalamic-pituitary-adrenal axis). This sophisticated feedback loop regulates cortisol production in response to your body's needs, time of day, and stress.

Cortisol is not the villain wellness culture makes it out to be. It's a critical hormone with multiple essential functions:

Energy Regulation

Cortisol mobilises glucose from stored energy, ensuring your brain and muscles have fuel. It's why you wake up alert—cortisol surges in the early morning. Without adequate cortisol, you'd struggle to maintain blood sugar levels.

Immune Modulation

Cortisol regulates inflammation and immune responses. Too little means unchecked inflammation; too much suppresses necessary immune function. This is why long-term steroid use increases infection risk—but also why steroids work as anti-inflammatory medications.

Blood Pressure

Cortisol helps maintain blood pressure and cardiovascular function. Deficiency causes dangerously low blood pressure—a hallmark of adrenal crisis. In severe adrenal insufficiency, blood pressure can drop to life-threatening levels.

Stress Response

During acute stress, cortisol helps your body respond appropriately. This is normal physiology—not a sign of "adrenal fatigue." Cortisol mobilises energy, sharpens focus, and temporarily suppresses non-essential functions like digestion and reproduction.

Key Point

People in Addisonian crisis—complete loss of cortisol production—don't just feel tired. They collapse, vomit, and can die without immediate medical intervention. This is not comparable to feeling "burnt out" after a stressful week at work.

The Circadian Rhythm Problem

Unlike biomarkers such as cholesterol or HbA1c that remain relatively stable throughout the day, cortisol follows a pronounced circadian rhythm. This is the fundamental reason why random cortisol testing is problematic.

Your cortisol level at 8am tells you almost nothing about your cortisol level at 8pm—and vice versa. This isn't a minor fluctuation; it's a dramatic, physiologically normal variation.

Cortisol's Daily Pattern

Peak (6-8am): Cortisol surges to its highest levels, helping you wake up and feel alert. This is the "cortisol awakening response" (CAR)—a rise of 50% or more in the first 30-45 minutes after waking.^[3]
Morning high: Levels remain elevated through the morning, supporting alertness and metabolism.
Gradual decline: Cortisol drops by 50-60% throughout the afternoon and evening.
Nadir (10pm-midnight): Cortisol reaches its lowest point, allowing melatonin to rise and enabling sleep.
Overnight rise: Levels slowly increase through the night, building toward the morning peak.

Morning cortisol can range from 5-25 μg/dL (140-700 nmol/L) depending on exact timing, stress, and individual variation. A value that's "normal" at 8am would be deeply concerning at midnight.

Why Single Cortisol Tests Fail

The dramatic daily variation in cortisol levels is precisely why a single random blood test is rarely clinically useful. Australian and international guidelines are clear on this point.

Limitations of Single Cortisol Testing

"Unless these factors are taken into consideration, random cortisol testing is rarely helpful." — PMC research review^[4]

Coefficient of variation 8-30%: Even in healthy individuals, hourly cortisol values vary markedly throughout the day.
No single cutoff works: Research shows that no single morning cortisol threshold is both adequately sensitive AND specific for diagnosing adrenal dysfunction.
Acute stress elevates results: Simply being anxious about a blood test can spike cortisol, creating false "highs."
False reassurance: A normal-looking random result may miss genuine adrenal problems that require dynamic testing to detect.

This is not us being unnecessarily cautious. This is what the medical literature states explicitly.

What Guidelines Say

The American Academy of Family Physicians (AAFP) explicitly recommends: "Don't use serum cortisol levels as initial screening for adrenal hyperfunction (Cushing syndrome); instead consider superior strategies."^[5]

For diagnosing Cushing's, late-night salivary cortisol, 24-hour urinary free cortisol, or the 1mg overnight dexamethasone suppression test are recommended instead of random serum cortisol.^[6]

If professional guidelines recommend against single cortisol testing for Cushing's syndrome—one of the conditions it's supposed to detect—what value does it have for investigating vague fatigue?

The "Adrenal Fatigue" Myth

Let's be direct: adrenal fatigue is not a real medical condition. It is a term popularised by alternative medicine practitioners with zero scientific basis.

Search "adrenal fatigue" online and you'll find countless wellness websites claiming your adrenal glands become "exhausted" from chronic stress, unable to produce adequate cortisol. Symptoms listed typically include fatigue, brain fog, salt cravings, difficulty waking, and reliance on caffeine.

We understand these symptoms are real and distressing. But the explanation being offered is not supported by medical science.

The Endocrine Society's Clear Position

"No scientific proof exists to support adrenal fatigue as a true medical condition." — Endocrine Society^[2]

The Endocrine Society is the world's oldest and largest organisation of endocrinologists. They do not mince words:

Adrenal fatigue is not a real medical condition
The adrenal glands do NOT get "fatigued" from mental or physical stress
"Adrenal fatigue" has not been recognised by any endocrinology society worldwide

This is not a matter of debate within mainstream medicine. It is settled.

The Systematic Review That Ended the Debate

A 2016 systematic review in BMC Endocrine Disorders examined 58 studies investigating the "adrenal fatigue" hypothesis and concluded:^[1]

"Adrenal fatigue does not exist... There is no substantiation that adrenal fatigue is an actual medical condition. Therefore, adrenal fatigue is still a myth."

The studies found no consistent pattern of cortisol abnormality in people with fatigue symptoms. Some had high cortisol, some had low, most had normal—exactly what you'd expect from random variation, not a real syndrome.

Fifty-eight studies. Zero evidence. The conclusion was unambiguous.

Why does this myth persist?

The symptoms are real—fatigue, brain fog, and feeling "burnt out" are genuine experiences affecting millions. People understandably want answers and solutions.

The healthcare system often fails to adequately investigate and address chronic fatigue, leaving patients frustrated and seeking alternative explanations.

Some wellness practitioners profit from expensive "adrenal support" supplement protocols, tests, and consultations based on this unproven diagnosis. An entire industry has been built around a condition that does not exist.

Danger of Unproven Treatments

The Endocrine Society warns that supplements sold as treatments for "adrenal fatigue" could be harmful:^[2]

Many supplements are not tested for safety by the TGA or FDA
If people take adrenal hormone supplements when they don't need them, their adrenal glands may stop working properly
Accepting an unproven diagnosis may delay finding the real cause of symptoms

Taking cortisol or cortisol-like compounds when you don't have adrenal insufficiency can suppress your own adrenal function, creating a real problem where none existed before.

What actually causes fatigue if not "adrenal fatigue"?

If you're experiencing persistent fatigue, common and treatable causes include:

Thyroid dysfunction (hypothyroidism)
Iron deficiency (with or without anaemia)
Vitamin D insufficiency
Vitamin B12 deficiency
Sleep disorders (including undiagnosed sleep apnoea)
Depression and anxiety
Poor sleep hygiene
Simply inadequate rest

These conditions have diagnostic criteria, evidence-based treatments, and are recognised by medical science. "Adrenal fatigue" has none of these.

Real Adrenal Disorders (Rare but Serious)

While "adrenal fatigue" is fiction, genuine adrenal disorders do exist. They are rare, have specific clinical presentations, and require specialised testing protocols for diagnosis.

These conditions are nothing like the vague symptoms attributed to "adrenal fatigue." They are serious, life-altering diseases.

Addison's Disease

Prevalence: 1 in 10,000 people
Cause: Autoimmune destruction of adrenal cortex (most common), infections (TB, fungal), or bilateral adrenalectomy
Symptoms: Severe and worsening fatigue, unintentional weight loss, loss of appetite, low blood pressure (especially on standing), salt cravings, darkening of skin (hyperpigmentation), nausea, vomiting, potentially life-threatening adrenal crisis
Diagnosis: Requires ACTH stimulation test (Synacthen test), morning cortisol, ACTH levels, and antibody testing
Key point: This is not "I'm tired after work." This is "I cannot stand up without feeling faint and I've lost 10kg without trying."

Cushing's Syndrome

Prevalence: 2-3 per million per year
Cause: Pituitary tumours (Cushing's disease), adrenal tumours, ectopic ACTH production, or long-term steroid medications
Symptoms: Weight gain (face/trunk), moon face, buffalo hump, thin skin, easy bruising, purple stretch marks (striae), muscle weakness, high blood pressure, glucose intolerance, facial hair growth in women
Diagnosis: Requires 24-hour urinary free cortisol, late-night salivary cortisol, or dexamethasone suppression test
Key point: Cushing's has specific, recognisable physical features. Your GP would suspect it based on appearance and examination findings—not a blood test.

Secondary Adrenal Insufficiency

Cause: Pituitary tumours, surgery, radiation, or long-term steroid use suppressing the HPA axis
Key difference from Addison's: No hyperpigmentation (ACTH not elevated), aldosterone usually preserved (so less salt craving and less severe blood pressure issues)
Diagnosis: Requires ACTH stimulation test with cortisol AND ACTH measurement; may need insulin tolerance test
Key point: Most commonly caused by long-term oral steroid use (prednisolone, dexamethasone). The treatment itself suppresses your HPA axis.

The Clinical Reality

These conditions are rare and have specific, recognisable clinical features. Your GP or endocrinologist would suspect these based on your symptoms, examination findings, and clinical presentation—not based on vague fatigue.

In Australia, the RACGP advises that investigation for adrenal insufficiency should be prompted by specific clinical features, not general tiredness.^[7]

If you simply feel tired and stressed, you almost certainly do not have Addison's disease or Cushing's syndrome. These are serious medical conditions with obvious clinical signs.

How Cortisol Is Properly Tested

When a genuine adrenal disorder is suspected based on clinical presentation, doctors use specific testing protocols—not random cortisol blood draws. These are called dynamic function tests because they assess how the adrenal glands respond to stimulation or suppression.

This is proper endocrinology. This is what separates evidence-based medicine from wellness industry guesswork.

For Suspected Adrenal Insufficiency (Addison's)

ACTH Stimulation Test (Synacthen Test)

Synthetic ACTH is injected, and cortisol measured at 0, 30, and 60 minutes
Healthy adrenals should respond by producing cortisol >500 nmol/L (18 μg/dL)
In Addison's disease, adrenals cannot respond—cortisol remains low despite stimulation
This test directly assesses adrenal reserve—your adrenals' ability to produce cortisol when called upon

Morning Cortisol (as screening only)

8-9am cortisol >420 nmol/L generally excludes adrenal insufficiency
Cortisol <100 nmol/L strongly suggests insufficiency
Values in between require the Synacthen test to clarify^[4]
This is the only context in which a single cortisol value has diagnostic utility—and even then, it's just a screen

For Suspected Cushing's Syndrome

Late-Night Salivary Cortisol

Cortisol should be very low at 11pm-midnight
Elevated late-night cortisol suggests loss of normal circadian rhythm—a hallmark of Cushing's
Two elevated samples on different nights are typically required
This tests the circadian rhythm directly—has the normal cortisol nadir been lost?

24-Hour Urinary Free Cortisol

Measures total cortisol output over a full day
Elevated levels suggest Cushing's syndrome
Integrates the entire day's cortisol production—far more informative than a single blood draw

Overnight Dexamethasone Suppression Test

Take 1mg dexamethasone at 11pm; measure cortisol at 8am next day
Healthy adrenals suppress cortisol to <50 nmol/L (1.8 μg/dL)
Failure to suppress suggests Cushing's^[6]
This tests the feedback loop—can the HPA axis respond to suppression signals?

Notice a pattern? None of these are "order a random cortisol and see what happens." They are structured, evidence-based protocols designed to answer specific clinical questions.

What to Expect from Your GP

If you approach your GP asking for cortisol testing because you're tired, expect some pushback—and understand this is good medicine, not dismissiveness.

A good GP will not simply tick boxes and order tests you request. They will assess whether those tests are clinically indicated.

A Good GP Will...

Assess your symptoms comprehensively: Fatigue has many causes; cortisol problems are one of the rarest
Test for common causes first: Thyroid function (TSH), iron studies (ferritin, iron, transferrin saturation), vitamin D, B12, full blood count, glucose/HbA1c
Evaluate sleep and mental health: Sleep disorders, depression, and anxiety are far more common causes of persistent fatigue than adrenal problems
NOT order random cortisol: Unless specific symptoms suggest Addison's or Cushing's
Explain why they're not ordering cortisol: The test won't change management and may create unnecessary anxiety

If your GP refuses to order a random cortisol test, they are practising evidence-based medicine. They are protecting you from unnecessary testing that will not help you.

If Your GP Does Suspect Adrenal Disease

They won't just order a random cortisol. Based on Australian guidelines:^[7]

For suspected Addison's: Morning cortisol (8-9am) as initial screen, then referral to endocrinologist for Synacthen test if concerning
For suspected Cushing's: 24-hour urinary cortisol, late-night salivary cortisol, or overnight dexamethasone suppression test
Specialist interpretation: Results require endocrinologist review—these are not simple "high" or "low" interpretations

Adrenal disorders are serious enough that they belong in specialist hands, not diagnosed via a random blood test from a wellness clinic.

Should You Test?

Skip If...

You're tired and wondering if you have "adrenal fatigue" (it doesn't exist)
You feel burnt out or stressed and want to check your cortisol (it won't help)
A wellness practitioner suggested cortisol testing without specific clinical findings
You want a general health check (many better markers exist)
You've read about "adrenal support" supplements online

Better approach: Test thyroid (TSH), iron studies, vitamin D, B12, and assess sleep quality and mental health first. These are evidence-based, actionable, and far more likely to identify a treatable cause.

Consider If...

You have unexplained weight loss with severe fatigue and consistently low blood pressure
You have darkening of your skin, especially in creases, gums, and scars (hyperpigmentation)
You have salt cravings with nausea, vomiting, and dizziness on standing
You have sudden significant weight gain with moon face, easy bruising, and purple stretch marks
You've taken long-term oral steroids (>3 weeks of prednisolone/dexamethasone) and are tapering or stopping
You have a known pituitary tumour

If you have these symptoms, your GP will order appropriate specialised tests—you won't need to request them.

The Bottom Line

Summary

Random cortisol blood tests have very limited clinical value. The hormone varies too dramatically throughout the day for a single measurement to be meaningful. This is not our opinion—this is what medical guidelines state explicitly.

"Adrenal fatigue" is not a recognised medical diagnosis. It does not exist. The Endocrine Society, systematic reviews, and medical literature are unambiguous on this point. A review of 58 studies concluded: "adrenal fatigue is still a myth." Your symptoms are real, but the explanation being offered is not supported by evidence.

Real adrenal disorders (Addison's, Cushing's) are rare and have specific clinical features. They require specialised dynamic testing—not a morning blood draw. If you had one of these conditions, your GP would know based on your symptoms and examination findings.

If you're persistently fatigued, investigate common causes first: Thyroid dysfunction, iron deficiency, vitamin D insufficiency, B12 deficiency, sleep disorders, and depression are all more likely and more treatable than adrenal problems.

Don't let wellness industry misinformation lead you to expensive, unnecessary testing—or worse, to unproven "adrenal support" supplements that may suppress your actual adrenal function while the real cause of your symptoms goes undiagnosed.

Evidence-based medicine is not about testing everything you can think of. It's about testing what will actually inform your treatment and improve your health. For cortisol, that threshold is rarely met.

Frequently Asked Questions

"Adrenal fatigue" is not a recognised medical diagnosis. It is a term popularised by alternative medicine practitioners suggesting that chronic stress exhausts the adrenal glands, reducing their ability to produce cortisol. However, a systematic review of 58 studies found no scientific evidence for this condition. The Endocrine Society—the world's largest endocrinology organisation—states that "no scientific proof exists to support adrenal fatigue as a true medical condition." The symptoms attributed to adrenal fatigue (fatigue, brain fog, salt cravings) are real but typically caused by other treatable conditions. Adrenal fatigue is a myth.

GPs don't routinely test cortisol for fatigue because: (1) Cortisol varies dramatically throughout the day, making single measurements difficult to interpret; (2) Real adrenal disorders are rare and have specific clinical features beyond just fatigue; (3) Fatigue is much more commonly caused by thyroid dysfunction, iron deficiency, vitamin D insufficiency, sleep disorders, or depression—all of which are more appropriately investigated first; (4) Medical guidelines explicitly recommend against using random cortisol as a screening test. If your GP suspects a genuine adrenal disorder based on your specific symptoms, they will order appropriate specialised tests.

Proper cortisol testing depends on the suspected condition. For suspected Cushing's syndrome (cortisol excess): late-night salivary cortisol, 24-hour urinary free cortisol, or overnight dexamethasone suppression test. For suspected Addison's disease (adrenal insufficiency): morning cortisol at 8-9am as a screen, followed by ACTH stimulation test (Synacthen test) if needed. These are dynamic function tests that assess how the adrenal glands respond to stimulation or suppression—far more informative than a single random blood draw. This is evidence-based endocrinology.

Acute stress temporarily elevates cortisol—this is normal and healthy physiology. Chronic stress can alter cortisol patterns, but this does NOT mean your adrenals are "fatigued" or failing. The HPA axis adapts to chronic stress in complex ways, but it does not "burn out." Testing random cortisol to assess stress is not clinically useful because normal cortisol varies dramatically throughout the day. If chronic stress is affecting your health, the focus should be on evidence-based stress management strategies and addressing any resulting mental health conditions like anxiety or depression—not chasing cortisol numbers.

True adrenal insufficiency (Addison's disease) is rare (1 in 10,000 people) but serious. Symptoms include: severe and worsening fatigue, unintentional weight loss, loss of appetite, nausea and vomiting, low blood pressure (especially dizziness on standing), salt cravings, darkening of the skin (hyperpigmentation in skin creases, gums, and scars), muscle weakness, and potentially life-threatening adrenal crisis during illness or stress. These symptoms are more specific and severe than the vague fatigue attributed to "adrenal fatigue." If you had Addison's disease, your GP would suspect it based on your clinical presentation—not based on general tiredness.

No. We cannot recommend supplements marketed for "adrenal support" or "adrenal fatigue." The Endocrine Society warns these products: (1) Are not tested for safety or efficacy by regulatory bodies; (2) May contain unlabelled ingredients including actual hormones; (3) Could suppress your adrenal glands if they contain cortisol or similar compounds, potentially causing real adrenal problems where none existed before. If you have genuine adrenal insufficiency diagnosed by proper testing, you need prescription cortisol replacement (hydrocortisone) under medical supervision—not supplements from a wellness website.

For persistent fatigue, evidence-based investigation should start with: Thyroid function (TSH, and T4 if TSH abnormal), Iron studies (ferritin is most sensitive for deficiency), Vitamin D, Vitamin B12, Full blood count (to check for anaemia), Blood glucose/HbA1c (to screen for diabetes), and consideration of sleep disorders (sleep apnoea is massively underdiagnosed) and mental health conditions (depression, anxiety). These causes are far more common than adrenal problems and have effective, proven treatments. If all of these are normal and you're still fatigued, further investigation is warranted—but adrenal problems remain unlikely.

The cortisol awakening response (CAR) is the natural surge in cortisol that occurs in the first 30-45 minutes after waking. In healthy individuals, cortisol increases by 50% or more during this period. While some functional medicine practitioners use CAR testing via multiple salivary samples, this test has limited clinical utility in mainstream medicine. A 2025 Bristol study even challenged the traditional understanding of CAR, suggesting waking may not be inherently stressful. This test is research-oriented and not recommended for investigating general fatigue. It will not diagnose "adrenal fatigue" because that condition does not exist.

Cortisol levels vary dramatically throughout the day and in response to many factors (stress, sleep, medications, time of day). A single "low" cortisol reading does not mean you have adrenal insufficiency. True adrenal insufficiency (Addison's disease) requires both clinical symptoms (severe fatigue, weight loss, low blood pressure, hyperpigmentation) AND confirmed failure of the adrenal glands on dynamic testing (ACTH stimulation test). A low random cortisol value in someone who feels tired but has no other symptoms is far more likely to be normal variation or poor test timing than genuine disease.

Disclaimer:This information is educational only and not medical advice. Results should be interpreted by your health practitioner in the context of your symptoms and health history. Treatment decisions should be made with your doctor or specialist.