BiomarkerHormones

Cortisol

The stress hormone — and why 'adrenal fatigue' isn't a diagnosis

Last reviewed: July 2026
Version: 1.0
Review cadence: Annually

Overview

Cortisol is the principal glucocorticoid, produced by the adrenal glands under instruction from the pituitary (via ACTH). It regulates glucose, blood pressure, and the immune and stress responses. It has a strong daily rhythm: highest shortly after waking, lowest around midnight.

Why it matters

Genuine disorders of cortisol are serious and eminently diagnosable. Too much (Cushing's syndrome) and too little (Addison's disease) are both real diseases with real tests and real treatments. But cortisol is also the centrepiece of a large wellness market built on a condition — 'adrenal fatigue' — that does not exist as a recognised diagnosis. Both facts need stating, because conflating them is how genuine adrenal insufficiency gets missed.

Start Here

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Typical Journey

How this usually unfolds

Measure it
Understand your result
See what raises and lowers it
Apply evidence-based interventions
Recheck on your review cadence

An orientation to how this topic is typically approached — not medical advice.

Optimal Range

Where the evidence points

Because of the diurnal rhythm, a single random cortisol is largely uninterpretable. Testing is time-specific — typically a morning (8–9am) serum cortisol — and abnormal results are followed with dynamic tests such as a short synacthen test or dexamethasone suppression.

Cortisol rises with any acute stress or illness, including the stress of having blood taken. Oestrogen (including the oral contraceptive pill) raises cortisol-binding globulin and therefore total cortisol, without any excess of active hormone. This is a hormone that punishes casual interpretation.

Clinical interpretation

Cortisol is never interpreted from a single number in isolation. A suspicion of deficiency (Addison's) is investigated with a morning cortisol followed by a stimulation test; a suspicion of excess (Cushing's) with suppression or 24-hour or late-night measurements. What cortisol testing does NOT do is diagnose 'adrenal fatigue' — a concept that has been examined and is not supported by evidence. Systematic review has found no consistent relationship between the salivary cortisol profiles sold as evidence for it and the symptoms attributed to it.

What raises and lowers it

Raises it

Acute stress and illness
Cushing's syndrome
Corticosteroid medication
Oestrogen / the oral contraceptive pill (raises total cortisol via binding globulin, not active hormone)
Depression and poor sleep (modestly)

Lowers it

Adrenal insufficiency (Addison's disease) — a serious, treatable condition
Pituitary disease
Abrupt withdrawal of long-term steroid therapy (a genuine medical emergency risk)
Ashwagandha (modest reductions reported in small trials)

Related Evidence

How this connects across BioSignal

Related conditions

Adrenal insufficiency
Cushing's syndrome

Related pharmaceuticals

Corticosteroids (suppress the axis — never stop abruptly)
Oral contraceptives (raise total, not active, cortisol)

Related lifestyle interventions

Sleep — the single most effective lever on the cortisol rhythm
Regular physical activity
Managing chronic psychological stress

Diagnostics

Morning (8–9am) serum cortisol
Short synacthen (ACTH stimulation) test — for suspected deficiency
Dexamethasone suppression / late-night salivary cortisol — for suspected excess
NOT: direct-to-consumer salivary cortisol 'adrenal fatigue' panels

Frequently asked questions

Do I have adrenal fatigue?

'Adrenal fatigue' is not a recognised medical diagnosis. The idea — that chronic stress exhausts the adrenal glands into underproducing cortisol — has been examined systematically and is not supported by the evidence. That does not mean your symptoms aren't real. Fatigue, poor sleep, and low mood are real, common, and deserve a proper diagnostic workup — one that a label like 'adrenal fatigue' actively prevents, and which could otherwise find genuine adrenal insufficiency, thyroid disease, anaemia, sleep apnoea, or depression.

Should I get a salivary cortisol test?

Not from a wellness company. Salivary cortisol has genuine, specific clinical uses — late-night salivary cortisol is a validated test for Cushing's syndrome. What it does not do is diagnose 'adrenal fatigue', because that is not a condition. If you have symptoms, the right answer is proper clinical assessment, not a mail-order panel.

Can I lower my cortisol with supplements?

Small trials suggest ashwagandha modestly lowers cortisol, but whether that produces any meaningful benefit is unknown — and a modestly lower number is not a health outcome. Sleep is by far the most powerful lever on the cortisol rhythm, and it is free.

Evidence summary

Cortisol testing is well validated for diagnosing genuine adrenal disease using time-specific and dynamic protocols. The 'adrenal fatigue' hypothesis has been examined in systematic review and is not supported: no consistent relationship exists between the cortisol profiles used to diagnose it and the symptoms attributed to it.

References & sources

Endocrine Society guidance on adrenal insufficiency and Cushing's syndrome
Systematic reviews examining the 'adrenal fatigue' hypothesis

Sources are named authoritative guidelines and scientific bodies. Biomarker pages present established clinical context; calibrated evidence verdicts on specific interventions live in the linked Signal Records.

Educational information — not medical advice

Reference ranges and interpretation vary by laboratory, assay, age, and individual. Use this to understand the science, then interpret your own results with a qualified clinician. See our Medical Disclaimer.

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