Lab result explainedHormonesLast updated November 8, 2026

Cortisol blood test: what high and low morning cortisol levels mean

Cortisol (morning serum cortisol) (Cortisol) · Hormone panel (usually ordered alone, with ACTH, or as part of a pituitary or adrenal work-up) · reported in mcg/dL (µg/dL) for serum; 1 mcg/dL = 27.6 nmol/L. Saliva in mcg/dL or nmol/L; urine in mcg per 24 hours

Cortisol is the main stress hormone, made by the adrenal glands on instruction from the pituitary hormone ACTH. It raises blood sugar, maintains blood pressure, damps inflammation and keeps you alert, and it follows a strong daily rhythm: highest in the first hour after waking, falling through the day, lowest around midnight. A cortisol blood test is almost always drawn at 8 am for that reason, and a normal morning serum cortisol is roughly 6 to 23 mcg/dL (165 to 635 nmol/L), with the exact range depending on the assay.

Most people searching for their result are worried about one of two opposite conditions. Too little cortisol (adrenal insufficiency, including Addison's disease) is suggested by a morning value below 3 mcg/dL and made unlikely by a value above 15 mcg/dL; anything between needs an ACTH stimulation test. Too much (Cushing's syndrome) cannot be diagnosed from a morning blood level at all, because stress, illness, obesity, depression and oral estrogen all push it up; it needs a late-night salivary cortisol, a 24-hour urine free cortisol or a dexamethasone suppression test.

The far larger group of readers has a value inside the normal range and is wondering whether 'high cortisol' explains tiredness, belly fat, poor sleep or anxiety. Cortisol does track chronic stress and short sleep, and some supplements and habits move it a little, but the effects seen in trials are modest and measured in people whose levels were already normal. A result in range does not need lowering; a result clearly outside it needs an endocrine work-up, not a supplement.

Cortisol at a glance

What it is: the adrenal stress hormone, driven by pituitary ACTH; peaks 30 to 45 minutes after waking and is near zero around midnight.
Normal 8 am serum cortisol: about 6–23 mcg/dL (165–635 nmol/L); many newer assays print 5–19 mcg/dL. Labs differ.
Low: below 3 mcg/dL at 8 am strongly suggests adrenal insufficiency; 3–15 is indeterminate and needs an ACTH stimulation test; above 15 makes it unlikely.
High: a raised morning level alone does not diagnose Cushing's syndrome; stress, illness, obesity, depression, alcohol, pregnancy and oral estrogen raise it. Screening uses late-night saliva (normal under about 0.1–0.15 mcg/dL), 24-hour urine or a 1 mg dexamethasone test (normal under 1.8 mcg/dL next morning).
Interferences: oral estrogen and pregnancy raise total cortisol by raising its carrier protein; high-dose biotin can falsely raise it on many immunoassays; prednisolone cross-reacts; dexamethasone and inhaled or topical steroids suppress it.
Next step: an abnormal result is repeated or followed by ACTH, an ACTH stimulation test, or Cushing's screening tests as appropriate; a random afternoon value is rarely interpretable.

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What Cortisol measures

The hypothalamus releases CRH, the pituitary responds with ACTH, and the adrenal cortex responds to ACTH by making cortisol within minutes. Cortisol then feeds back to switch both off. This axis is pulsatile and strongly circadian, timed to the sleep-wake cycle rather than the clock: the peak comes 30 to 45 minutes after waking (the cortisol awakening response), with a decline through the day to a nadir in the first hours of sleep. Night-shift workers have the pattern shifted, which is why a 'morning' sample from someone who slept all day can look low.

A serum cortisol measures total cortisol, about 90 percent of which is bound to cortisol-binding globulin (CBG) and albumin. Anything that changes CBG changes the total without changing the free, active hormone: oral estrogen (the combined pill, oral HRT) and pregnancy roughly double CBG and can push total cortisol to 30 to 50 mcg/dL in a healthy woman, while cirrhosis, nephrotic syndrome and critical illness lower CBG and make total cortisol read low. Salivary cortisol measures the free fraction and is unaffected by CBG, which is one reason it is used for the late-night test.

Most labs use an immunoassay. Synthetic glucocorticoids cross-react to different degrees: prednisolone and methylprednisolone read as cortisol and give falsely high values, while dexamethasone does not cross-react but suppresses the real thing. Biotin above about 5 to 10 mg a day (common in hair and nail supplements) interferes with many immunoassay platforms and, for competitive assays like cortisol, typically produces a falsely high result; stop biotin for at least 48 to 72 hours before the test. LC-MS/MS avoids these problems and is increasingly used for salivary and urine cortisol.

Normal range for Cortisol

Reference ranges vary between labs and by age, sex and pregnancy. Use the range printed on your own report.

Group	Typical range (mcg/dL (µg/dL) for serum; 1 mcg/dL = 27.6 nmol/L. Saliva in mcg/dL or nmol/L; urine in mcg per 24 hours)	Notes
8 am serum cortisol, typical reference range	6–23 mcg/dL (165–635 nmol/L)	Older polyclonal assays; newer monoclonal assays and LC-MS/MS run lower, often 5–19 mcg/dL. Use the range printed on your report.
4 pm serum cortisol	About 3–13 mcg/dL (roughly half the morning value)	An afternoon value is rarely useful on its own.
Midnight serum cortisol (asleep, inpatient)	Below 1.8 mcg/dL (50 nmol/L) in healthy people	A sleeping midnight serum cortisol above 1.8 mcg/dL is abnormal; an awake value above 7.5 mcg/dL supports Cushing's syndrome.
Adrenal insufficiency likely	8 am serum cortisol below 3 mcg/dL (80 nmol/L)	Endocrine Society 2016; with a high ACTH this is primary (Addison's), with a low or normal ACTH it is secondary (pituitary or steroid-related).
Adrenal insufficiency unlikely	8 am serum cortisol above 15 mcg/dL (415 nmol/L); some centres use 13–14 on newer assays	Values between 3 and 15 mcg/dL need a 250 mcg cosyntropin (ACTH) stimulation test: a 30- or 60-minute cortisol of 18 mcg/dL or more (14–15 on newer assays) is a normal response.
Late-night salivary cortisol (11 pm to midnight)	Below about 0.09–0.15 mcg/dL (2.5–4 nmol/L), assay dependent	Two collections on separate nights; one of the three first-line screens for Cushing's syndrome.
1 mg overnight dexamethasone suppression test	8 am cortisol below 1.8 mcg/dL (50 nmol/L) after 1 mg dexamethasone at 11 pm	Failure to suppress suggests Cushing's syndrome; false positives with oral estrogen, drugs that speed dexamethasone metabolism, and missed doses.
24-hour urine free cortisol	Below about 45–50 mcg/24 hours on LC-MS/MS; up to 100 on some immunoassays	Values more than 3 to 4 times the upper limit are strongly suggestive of Cushing's; two collections are recommended.
Pregnancy and oral estrogen	Total serum cortisol 2 to 3 times usual (often 25–50 mcg/dL)	Carrier-protein effect; salivary and urine free cortisol are less affected. Stop oral estrogen for 6 weeks before Cushing's testing if possible.

High cortisol

A morning serum cortisol above the reference range is common and usually does not mean Cushing's syndrome. The axis is designed to respond to stress, so acute illness, pain, a difficult blood draw, a poor night's sleep, a fast before the test, intense exercise the evening before, depression, alcohol use and simply being anxious about the result all raise it. Obesity and poorly controlled diabetes raise it modestly. Oral estrogen and pregnancy roughly double the total by raising cortisol-binding globulin, and prednisolone or hydrocortisone taken that morning will be measured as cortisol. Most single high values resolve on a repeat taken calmly, fasting, at 8 am.

Cushing's syndrome, true chronic cortisol excess, is rare (a few cases per million per year for the pituitary form) but important, because untreated it causes diabetes, hypertension, fractures and a shortened life. The commonest cause by far is prescribed glucocorticoids, including high-dose inhaled, injected, topical or herbal products contaminated with steroids. Internal causes are a pituitary adenoma making ACTH (Cushing's disease, about 70 percent of internal cases), a cortisol-producing adrenal tumour (about 20 percent) and ectopic ACTH from a lung or other tumour (about 10 percent). The diagnosis rests on the loss of the daily rhythm and the loss of suppressibility, not on the 8 am level.

People with depression, alcohol dependence, obesity, poorly controlled diabetes and severe stress can have mildly abnormal screening tests without a tumour (sometimes called pseudo-Cushing's or physiological hypercortisolism). Separating this from true Cushing's takes repeat testing after the underlying condition is treated and sometimes specialist tests. An ACTH level then tells whether a confirmed excess is adrenal (ACTH suppressed, below 10 pg/mL) or ACTH-driven, and imaging follows.

Common causes

Stress of the blood draw, acute illness, pain or poor sleep
The axis responds within minutes; a difficult venepuncture, a night awake or a flu can double the morning value. This is why one high result is repeated under calm, rested, fasting conditions before anything is concluded.
Prescribed glucocorticoids
Prednisolone, methylprednisolone and hydrocortisone cross-react with or are cortisol and read high; dexamethasone reads low but causes Cushing's features. Any form counts: tablets, high-dose inhalers, joint injections, potent skin creams and some imported herbal or 'joint pain' products.
Oral estrogen and pregnancy
The combined pill, oral HRT and pregnancy increase cortisol-binding globulin, roughly doubling total cortisol and causing false-positive dexamethasone suppression tests. Transdermal estrogen has much less effect.
Depression, anxiety and chronic psychological stress
Major depression raises evening cortisol and flattens the daily rhythm; about half of people with severe depression fail to suppress on dexamethasone. Levels normalise as the depression improves.
Alcohol excess
Heavy drinking stimulates CRH and can produce a Cushing's-like picture (alcohol-induced pseudo-Cushing's) with high cortisol, facial redness and central weight gain that reverses within weeks of abstinence.
Obesity, insulin resistance and poorly controlled diabetes
Urinary and evening cortisol run modestly higher with visceral obesity and hyperglycaemia; the rise is small and does not reach Cushing's levels but can confuse screening tests.
Cushing's disease (pituitary ACTH-secreting adenoma)
Usually a small adenoma under 1 cm; cortisol loses its rhythm so the midnight value stays high, 24-hour urine cortisol is raised and the 1 mg dexamethasone test fails to suppress. About 70 percent of internal Cushing's; women affected 3 to 4 times more often than men.
Adrenal adenoma or carcinoma
Makes cortisol independently of ACTH, so ACTH is suppressed (often below 5 to 10 pg/mL). Mild autonomous cortisol secretion is found in 5 to 30 percent of incidentally discovered adrenal nodules.
Ectopic ACTH from a tumour
Small-cell lung cancer, bronchial carcinoid, thymic and pancreatic neuroendocrine tumours; often very high cortisol with rapid muscle wasting, low potassium and darkening skin rather than classic weight gain.
Biotin supplements and assay interference
Biotin at 5 to 10 mg a day or more (common in hair, skin and nail products) causes falsely high cortisol on many competitive immunoassays; stop it 48 to 72 hours before testing. Rare heterophile antibodies also interfere.

Symptoms that can go with it

Usually none when the rise is from stress, sleep loss or estrogen
Weight gain in the face, neck and trunk with thin arms and legs; a rounded 'moon' face and a fat pad between the shoulders
Wide purple stretch marks (over 1 cm), thin skin, easy bruising and slow wound healing
Muscle weakness, particularly difficulty rising from a chair or climbing stairs
High blood pressure, new or worsening diabetes, low potassium
Irregular periods, acne and excess hair in women; low libido and erectile dysfunction in men
Low mood, anxiety, irritability, poor memory and insomnia
Bone loss and fractures, kidney stones, frequent infections

Low cortisol

A low morning cortisol means the adrenal glands may not be making enough, which can be life-threatening if it is real. Below 3 mcg/dL at 8 am is strongly suggestive of adrenal insufficiency; 3 to 15 mcg/dL is indeterminate and is followed by an ACTH stimulation test, in which a synthetic ACTH injection should raise cortisol to at least 18 mcg/dL (about 14 to 15 on newer assays) within 30 to 60 minutes. A value that fails to rise confirms the diagnosis, and a paired ACTH level then separates the two types.

Primary adrenal insufficiency (Addison's disease) is destruction of the adrenal glands themselves, in developed countries usually autoimmune, with a high ACTH, low sodium, high potassium, salt craving and darkening of the skin creases, gums and scars. Secondary insufficiency is a failure of the pituitary to make ACTH, and its commonest cause by far is suppression from glucocorticoid medication: anyone who has taken the equivalent of 5 mg or more of prednisolone a day for more than 3 to 4 weeks, including high-dose inhaled, injected or potent topical steroids, can have a low cortisol for weeks to months after stopping. Other secondary causes are pituitary tumours and surgery, head injury, Sheehan's syndrome, long-term opioid use and immune checkpoint inhibitor cancer drugs.

Not every low value is disease. Shift workers and people who slept late have a shifted peak; low cortisol-binding globulin from liver disease, nephrotic syndrome or critical illness lowers the total but not the free hormone; a dose of dexamethasone (including in some anti-nausea and steroid-injection regimens) suppresses the result without harming the adrenals; and some labs' newer assays read 20 to 30 percent lower than the old ranges. Anyone with a low cortisol and vomiting, dizziness, low blood pressure or confusion, however, needs same-day assessment for adrenal crisis.

Common causes

Recent or current glucocorticoid treatment
The most common cause. Prednisolone, dexamethasone, hydrocortisone, high-dose inhaled steroids (fluticasone in particular), steroid injections and potent creams suppress ACTH; recovery after a long course can take 6 to 12 months. Dexamethasone also does not register on the assay, so the measured value is low.
Autoimmune Addison's disease
Antibodies against the adrenal enzyme 21-hydroxylase destroy the cortex; accounts for 80 to 90 percent of primary adrenal insufficiency in high-income countries. Often clusters with autoimmune thyroid disease, type 1 diabetes, vitiligo and pernicious anemia.
Pituitary disease
Pituitary tumours, surgery or radiation, Sheehan's syndrome after a postpartum haemorrhage, lymphocytic hypophysitis, head injury and infiltrative diseases lower ACTH; other pituitary hormones (TSH, LH/FSH, growth hormone) are often low too.
Immune checkpoint inhibitors
Ipilimumab, nivolumab, pembrolizumab and related cancer drugs cause hypophysitis or adrenalitis in a few percent of patients, typically within the first few months; the resulting insufficiency is usually permanent.
Long-term opioid use
Opioids suppress the hypothalamic-pituitary-adrenal axis; studies find a suboptimal cortisol response in 10 to 20 percent of people on long-term opioids, which improves if the dose can be reduced.
Infection, bleeding or metastases in the adrenals
Tuberculosis is the leading cause of Addison's worldwide; HIV-related infections, fungal infections, bilateral adrenal haemorrhage (anticoagulants, sepsis, antiphospholipid syndrome) and metastatic cancer also destroy the glands.
Congenital adrenal hyperplasia and other genetic causes
Classic 21-hydroxylase deficiency presents in infancy; adrenoleukodystrophy should be considered in boys and young men with Addison's disease.
Low cortisol-binding globulin
Cirrhosis, nephrotic syndrome, severe illness and rare inherited CBG deficiency lower total cortisol while free cortisol is normal; salivary or free cortisol clarifies.
Shifted sleep schedule or sample taken at the wrong time
Night-shift workers who slept during the day have their peak hours later; an '8 am' sample drawn a few hours after they fell asleep is at their nadir. Tell the lab when you woke.
Drugs that speed cortisol breakdown or block its synthesis
Ketoconazole, fluconazole at high dose, etomidate, metyrapone, mitotane and osilodrostat block synthesis; phenytoin, rifampicin and carbamazepine speed clearance and can unmask marginal reserve.

Symptoms that can go with it

Profound fatigue, weakness and weight loss that build over months
Nausea, loss of appetite, abdominal pain and vomiting
Dizziness or fainting on standing from low blood pressure
Salt craving and darkening of skin creases, knuckles, gums, scars and sun-exposed areas (primary Addison's only)
Low blood sugar, especially in children and after fasting
Muscle and joint aches, low mood and irritability
Loss of pubic and underarm hair in women (adrenal androgens fall)
Adrenal crisis: severe vomiting, collapse, confusion, very low blood pressure, often triggered by infection, surgery or stopping steroids; this is an emergency

Read it alongside

ACTH — the deciding test once cortisol is abnormal: high ACTH with low cortisol is Addison's disease; low ACTH with low cortisol is pituitary or steroid-related; suppressed ACTH with high cortisol points to an adrenal tumour.
Sodium and potassium — low sodium and high potassium with low cortisol suggest primary adrenal insufficiency with aldosterone loss; low potassium with very high cortisol suggests ectopic ACTH.
Glucose and A1C — cortisol raises blood sugar; low glucose supports insufficiency, new diabetes supports Cushing's.
TSH and free T4 — adrenal and thyroid autoimmunity travel together, and thyroid hormone should not be started before cortisol deficiency is treated, since it can precipitate an adrenal crisis.
DHEA-S — made by the adrenal cortex under ACTH; low in both forms of adrenal insufficiency and in people on steroids, high in some adrenal tumours.
Renin and aldosterone — high renin with low aldosterone confirms the mineralocorticoid deficiency of Addison's disease.
Eosinophils and lymphocytes — cortisol suppresses eosinophils; a high eosinophil count fits insufficiency and a very low one fits excess.
Prolactin, LH, FSH, IGF-1 — checked when pituitary disease is suspected as the cause of low cortisol.

What usually happens next

A single abnormal morning cortisol is usually repeated at 8 am, fasting, rested, having stopped biotin for 72 hours and after noting every steroid-containing medicine, inhaler, cream, injection and oral estrogen you use.
A low or indeterminate value (3 to 15 mcg/dL) is followed by a paired ACTH level and a 250 mcg cosyntropin stimulation test, often within days; if adrenal insufficiency is confirmed, expect sodium, potassium, renin, aldosterone, 21-hydroxylase antibodies and sometimes adrenal imaging or a pituitary MRI.
If Cushing's syndrome is the question, a morning value is not enough: ask for two late-night salivary cortisols, two 24-hour urine free cortisols or a 1 mg overnight dexamethasone suppression test, and for the results to be interpreted in light of estrogen use, depression, alcohol and sleep pattern.
If you have recently taken or tapered glucocorticoids, the test may need to be timed before the morning dose, and recovery may be tracked with repeat 8 am cortisols every few months rather than treated as permanent disease.
Ask whether your result was drawn at your personal 'morning' (within two hours of waking) rather than the clock's, especially if you work nights.
For a value inside the normal range with stress-related symptoms, the useful conversation is about sleep, alcohol, caffeine, activity and mood rather than further cortisol testing; home saliva 'cortisol curve' kits are not validated for diagnosis.

Diet, lifestyle and natural levers with evidence

What can move Cortisol once the cause is known. Nothing here replaces finding the cause.

Sleep and a regular wake time

Moderate evidence

Sleep loss raises next-evening cortisol by roughly 35 to 45 percent in controlled studies and flattens the normal daily decline, while a consistent wake time anchors the morning peak. Treating insomnia with cognitive behavioural therapy lowers evening cortisol modestly in small trials. This is the lever with the most consistent effect on the daily cortisol pattern in people without endocrine disease.

Mindfulness, meditation and yoga practice

Moderate evidence

A 2017 meta-analysis of 45 randomised trials of meditation found a small but significant reduction in cortisol (standardised effect about 0.2 to 0.3), and a 2022 review of mindfulness-based stress reduction found reductions in morning or diurnal cortisol in about half of the trials, mostly in stressed or clinical groups. Effects are real but small, typically a 10 to 20 percent lower salivary value, and absent in many studies of healthy people.

Regular moderate exercise (and not over-training)

Moderate evidence

Trained people have a lower cortisol response to the same mental or physical stressor, and regular aerobic exercise programmes lower resting evening cortisol in overweight adults by small amounts. A single hard session raises cortisol two- to threefold for an hour or two, and prolonged high-volume training with inadequate recovery and fuel raises resting levels, so the dose matters.

Do not have cortisol measured within 24 hours of intense or prolonged exercise.

Ashwagandha

Preliminary evidence

The best-known 'cortisol-lowering' supplement. In a 60-day trial of 64 chronically stressed adults, 300 mg of root extract twice daily lowered morning serum cortisol by 28 percent versus 8 percent on placebo; a 2019 trial of 60 adults found 240 mg a day lowered morning cortisol by 23 percent versus placebo, and a 2023 systematic review of 9 small trials found reductions of 11 to 32 percent. The trials are small (30 to 130 people), 6 to 12 weeks long, mostly industry-funded and conducted in people with normal cortisol and self-reported stress; a 25 percent fall from 15 mcg/dL is still well within the normal range, and there is no evidence it helps Cushing's syndrome or harms a low level.

Case reports of liver injury; can raise thyroid hormone levels; avoid in pregnancy, autoimmune disease flares and with sedatives or immunosuppressants. Stop it before cortisol testing.

Omega-3 fatty acids

Preliminary evidence

In a 4-month randomised trial of 138 sedentary overweight adults, 2.5 g a day of EPA plus DHA reduced the cortisol response to a laboratory stress test by about 19 percent compared with placebo, and lowered inflammatory markers; a few smaller trials show similar blunting of stress-induced cortisol, but resting morning cortisol is largely unchanged.

Doses above 3 g a day can increase bleeding tendency and have been linked with atrial fibrillation in some trials.

Rhodiola, phosphatidylserine and L-theanine

Preliminary evidence

Rhodiola (576 mg a day for 28 days) lowered the cortisol awakening response slightly in a 60-person trial of people with fatigue; phosphatidylserine (400 to 800 mg) blunted exercise- and stress-induced cortisol in trials of 20 to 80 people but did not change resting levels; L-theanine (200 mg) reduced salivary cortisol after an acute stress task in small crossover studies. Each has one or two small positive trials and no evidence in people with abnormal cortisol.

Rhodiola can interact with antidepressants and is stimulating for some people; buy from reputable suppliers, as adulteration is common.

When to see a clinician promptly

Low cortisol or known adrenal insufficiency with vomiting, severe weakness, confusion, fainting or very low blood pressure: possible adrenal crisis, call emergency services; it is fatal without urgent intravenous hydrocortisone and fluids.
An 8 am cortisol below 3 mcg/dL, or between 3 and 15 with fatigue, weight loss, nausea, dizziness on standing or darkening skin: needs an ACTH stimulation test within days, not weeks.
You have recently stopped or tapered steroid tablets, injections or high-dose inhalers and feel exhausted, nauseated or faint, especially during an infection.
Rapid central weight gain with thin limbs, wide purple stretch marks, easy bruising, new high blood pressure or diabetes, and muscle weakness: Cushing's screening is needed even if the morning cortisol is normal.
New severe headache or loss of side vision with any abnormal cortisol: possible pituitary tumour.
A persistently abnormal cortisol with low sodium, high potassium or low blood sugar on routine tests.

Frequently asked questions

What is a normal cortisol level at 8 am?

Most labs quote about 6 to 23 mcg/dL (165 to 635 nmol/L) for an 8 am serum cortisol, though newer assays often print 5 to 19 mcg/dL, so use the range on your own report. For the specific question of adrenal insufficiency, the Endocrine Society treats a morning value above 15 mcg/dL as making it unlikely and below 3 mcg/dL as strongly suggestive, with 3 to 15 needing a stimulation test. The value must be drawn within about two hours of your usual waking time to mean anything.

Does a high morning cortisol mean I have Cushing's syndrome?

No. A single morning value is not used to diagnose Cushing's because stress, illness, poor sleep, obesity, depression, alcohol, pregnancy and oral estrogen all raise it. Cushing's is a loss of the daily rhythm and of the ability to suppress, so it is screened for with two late-night salivary cortisols, two 24-hour urine free cortisols or a 1 mg overnight dexamethasone test. If your morning value is high but you have none of the physical features (central weight gain, purple stretch marks, muscle weakness, bruising), the most likely explanation is one of the ordinary ones.

What does a cortisol saliva test show?

Saliva measures free cortisol, the active fraction, and is collected at home at 11 pm to midnight to catch the daily low point. In healthy people it is very low (under about 0.1 to 0.15 mcg/dL depending on the assay); in Cushing's syndrome it stays high. Two samples on different nights are standard. Multi-point 'cortisol curve' saliva kits sold online use the same chemistry but have no validated reference ranges for diagnosing 'adrenal fatigue', which is not a recognised condition; a flat or odd-looking curve on one of those kits is not a diagnosis.

How do I lower cortisol?

If your cortisol is truly high because of Cushing's syndrome or steroid medication, supplements will not fix it and you need endocrine care. If it is in range and you are trying to feel less stressed, the measures with evidence are sleep (7 to 9 hours with a fixed wake time), regular moderate exercise, limiting alcohol and late caffeine, and mindfulness or meditation practice; each lowers cortisol by small amounts, typically 10 to 25 percent, in trials. Ashwagandha has several small trials showing reductions of 11 to 32 percent over 6 to 12 weeks, but the studies are short, mostly industry-funded and in people whose levels were already normal.

What are the symptoms of low cortisol?

Fatigue that builds over weeks to months, weight loss, nausea, loss of appetite, abdominal pain, dizziness on standing, salt craving and low blood sugar; in Addison's disease the skin creases, gums and scars darken. The danger is adrenal crisis, usually triggered by an infection, injury or surgery, with vomiting, collapse and very low blood pressure. People who have recently stopped a long course of steroids are at particular risk and may not realise their adrenals are suppressed.

Can stress and anxiety raise cortisol levels on a blood test?

Yes. The axis responds within minutes, so anxiety about the test, a painful needle, a poor night's sleep, pain, fasting or an argument that morning can push an 8 am value from 12 to 25 mcg/dL. Chronic stress and depression raise evening levels and flatten the daily rhythm. These effects are real but do not usually produce the grossly abnormal, non-suppressible pattern of Cushing's syndrome, which is why repeat testing under calm conditions and the specific screening tests are used.

Do birth control pills or HRT affect cortisol?

Oral estrogen (the combined pill, oral HRT) roughly doubles cortisol-binding globulin, so total serum cortisol can read 25 to 50 mcg/dL in a healthy woman, and the dexamethasone suppression test gives false positives. Free cortisol in saliva or urine is much less affected. If Cushing's testing is planned, guidelines suggest stopping oral estrogen for about 6 weeks first, or using salivary and urine tests instead. Transdermal estrogen has little effect.

Does biotin affect a cortisol test?

It can. Biotin at doses of 5 to 10 mg a day or more, common in hair, skin and nail supplements, interferes with many immunoassay platforms. For cortisol, which is measured by a competitive immunoassay on most analysers, the interference typically produces a falsely high result, though the direction depends on the assay. Stop biotin for at least 48 to 72 hours before the test and tell the lab; ordinary multivitamin doses (30 to 100 mcg) do not interfere.

References

Cortisol test. MedlinePlus, US National Library of Medicine (2024)View source
Bornstein SR, Allolio B, Arlt W, et al.. Diagnosis and treatment of primary adrenal insufficiency: an Endocrine Society clinical practice guideline. Journal of Clinical Endocrinology and Metabolism (2016)View source
Nieman LK, Biller BM, Findling JW, et al.. The diagnosis of Cushing's syndrome: an Endocrine Society clinical practice guideline. Journal of Clinical Endocrinology and Metabolism (2008)View source
Fleseriu M, Auchus R, Bancos I, et al.. Consensus on diagnosis and management of Cushing's disease: a guideline update. Lancet Diabetes and Endocrinology (2021)
El-Farhan N, Rees DA, Evans C. Measuring cortisol in serum, urine and saliva: are our assays good enough?. Annals of Clinical Biochemistry (2017)
Biotin interference with laboratory tests: FDA safety communication. US Food and Drug Administration (2019)
Chandrasekhar K, Kapoor J, Anishetty S. A prospective, randomized double-blind, placebo-controlled study of safety and efficacy of a high-concentration full-spectrum extract of ashwagandha root in reducing stress and anxiety in adults. Indian Journal of Psychological Medicine (2012)
Lopresti AL, Smith SJ, Malvi H, Kodgule R. An investigation into the stress-relieving and pharmacological actions of an ashwagandha (Withania somnifera) extract: a randomized, double-blind, placebo-controlled study. Medicine (Baltimore) (2019)
Della Porta M, Maier JA, Cazzola R. Effects of Withania somnifera on cortisol levels in stressed human subjects: a systematic review. Nutrients (2023)
Madison AA, Belury MA, Andridge R, et al.. Omega-3 supplementation and stress reactivity of cellular aging biomarkers: an ancillary substudy of a randomized, controlled trial in midlife adults. Molecular Psychiatry (2021)
Pascoe MC, Thompson DR, Jenkins ZM, Ski CF. Mindfulness mediates the physiological markers of stress: systematic review and meta-analysis. Journal of Psychiatric Research (2017)
Addison disease. Merck Manual Professional Version (2024)

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This page is educational and is not medical advice or a diagnosis. Lab results have to be interpreted together with your history, symptoms and other results by a clinician who knows you. Do not start or stop a supplement to change a lab value before the cause is known.