Cortisol, adrenal fatigue and what is real

Cortisol has become the explanation of choice for tiredness, weight gain and stress, which has produced a substantial market and a good deal of confusion.

What cortisol actually does

It is a glucocorticoid produced by the adrenal cortex under control of the pituitary and hypothalamus.

It mobilises glucose, modulates immune function and inflammation, affects blood pressure, and influences mood and cognition.

It follows a pronounced daily rhythm, peaking in the half hour after waking and declining through the day to a low in the early part of the night — which is why a single measurement without a time attached tells you nothing.

It rises acutely with stress of any kind, including physical illness, exercise and the venepuncture used to measure it.

The conditions that genuinely exist

Cushing's syndrome: genuine cortisol excess, most commonly from prescribed steroids and less commonly from a pituitary or adrenal tumour.

Features include central weight gain with thin limbs, a rounded face, purple stretch marks, easy bruising, thin skin, proximal muscle weakness, high blood pressure and glucose intolerance.

It is rare and it looks distinctive.

Adrenal insufficiency, including Addison's disease: genuine cortisol deficiency, which is uncommon and potentially life-threatening.

Features include profound fatigue, weight loss, low blood pressure, dizziness on standing, nausea, salt craving and in primary disease, skin darkening.

It is diagnosed with specific tests including a synacthen stimulation test, and treated with replacement steroids for life.

An adrenal crisis is a medical emergency.

Secondary adrenal insufficiency from suddenly stopping long-term steroid treatment, which is the most common cause and the reason steroids are tapered rather than stopped.

Adrenal fatigue

The proposed condition in which chronic stress supposedly exhausts the adrenal glands, producing fatigue and a range of non-specific symptoms.

A systematic review examining the evidence found no consistent support for its existence, with studies using varied and unvalidated testing methods producing contradictory results.

Endocrine societies have issued statements stating that it is not a recognised diagnosis.

This matters for two reasons.

The first is that people given this label are frequently sold supplements, restrictive protocols and in some cases unnecessary steroid treatment, which carries real risk including suppression of their own axis.

The second is that being given a false explanation stops the search for the real one, and the symptoms attributed to it — fatigue, poor sleep, low mood, brain fog — have a long list of genuine causes.

What to investigate instead

When someone presents with persistent fatigue, the differential is long and largely testable.

Anaemia and iron deficiency, which is extremely common and frequently missed when haemoglobin is normal but ferritin is low.

Thyroid disease.

Diabetes.

Sleep apnoea, which is a leading cause of fatigue and is substantially underdiagnosed.

Depression and anxiety.

Coeliac disease.

Vitamin B12 and vitamin D deficiency.

Chronic infection and inflammatory conditions.

Medication effects.

Perimenopause.

Chronic insufficient sleep, which remains the most common explanation of all.

And myalgic encephalomyelitis or chronic fatigue syndrome, which is a genuine and disabling condition, is not the same as adrenal fatigue, and has its own diagnostic criteria including post-exertional symptom exacerbation.

Cortisol testing sold directly

Saliva cortisol panels sold to consumers are difficult to interpret without clinical context, are affected by numerous factors, and rarely lead to any action that a clinician would take.

Hair cortisol is a research tool rather than a clinical one.

Where genuine adrenal disease is suspected, the tests used are specific, timed and generally involve stimulation or suppression rather than a single level.

What actually lowers a chronically activated stress response

Since the underlying concern is usually real even when the label is not.

Sleep, physical activity, reducing alcohol and caffeine, addressing the source of the stress where possible, social connection, and interventions with evidence such as mindfulness-based stress reduction.

These are unglamorous, are free, and have a considerably better evidence base than any supplement marketed for adrenal support.

General information only, not medical advice. Consult a qualified clinician about persistent fatigue — do not take steroids or adrenal supplements without proper diagnosis.