Clinical Biochemistry

Adrenal Fatigue Isn't Real. What You Have Is Still Real.

Stephen Duncan FDN-P BSc Hons MSc  ·  7 min read

If you've been told you have adrenal fatigue, two things are true at once, and most people only ever get told one of them.

The first is that adrenal fatigue is not a recognised medical condition. It has never been accepted by any endocrinology society. In 2016, Cadegiani and Kater published a systematic review in BMC Endocrine Disorders with a title that leaves little room for interpretation — Adrenal fatigue does not exist — and concluded that there is no substantiation for it as an actual medical condition.

The second is that you are not imagining your symptoms, and something measurable is very probably going on.

Both of those need saying together, because saying only the first is how people end up dismissed, and saying only the second is how they end up sold something.

What the theory actually claims

The adrenal fatigue model goes like this. Prolonged stress makes the adrenal glands work continuously. Eventually they tire out, like a muscle worked past exhaustion, and can no longer produce enough cortisol. The result is fatigue, poor stress tolerance, salt cravings, difficulty waking, and an afternoon crash.

It's an intuitive model. It's also, as a description of adrenal physiology, wrong.

Adrenal glands don't tire. There is a condition where the adrenal cortex genuinely fails — primary adrenal insufficiency, Addison's disease — and it is a serious, potentially life-threatening illness with a specific presentation, specific biochemistry, and a specific diagnostic test. It is nothing like the picture described above, and people with genuine adrenal insufficiency are not helped by being lumped in with a wellness label.

That's the first reason the terminology matters. The second is that "your adrenals are tired" implies a fix — support the adrenals, usually with something purchasable — that doesn't follow from what's actually happening.

What the review actually said

It's worth reading the systematic review properly rather than taking the headline, because it's more interesting than the title suggests.

The authors reviewed the literature and found conflicting results across studies, poor quality assessment of fatigue, and — this one is important — "the use of an unsubstantiated methodology in terms of cortisol assessment." A great deal of the research supposedly demonstrating adrenal fatigue was built on cortisol testing that endocrinologists don't accept as valid.

But they also made a recommendation that rarely gets quoted. They wrote that the terminology should be normalised, with a suitable name given for the purported condition, because "adrenal fatigue" has been stigmatised and lacks proper scientific support. And they noted that the studies which did look seriously at the HPA axis and fatigue states used the term burnout instead.

So the authors of the paper most often cited to dismiss all of this are not saying nothing happens to stressed people. They're saying the name is wrong, the methodology has been poor, and the phenomenon deserves proper investigation under a proper name.

I agree with all three.

What is actually measurable

The adrenal glands are the last stop in a three-part system, not the whole of it.

The hypothalamus releases CRH. The pituitary responds with ACTH. The adrenal cortex responds by producing cortisol. Cortisol then feeds back to the hypothalamus and pituitary to dampen the signal. That's the HPA axis, and it is a regulatory loop rather than a tank that empties.

When this system is disturbed by prolonged stress, what changes is the regulation, not the capacity. Specifically:

The rhythm shifts. Cortisol should be highest shortly after waking and lowest late at night. Under chronic stress that curve flattens, inverts, or develops a mid-afternoon dip. The total amount produced across the day can be entirely normal while the timing is wrong — and the timing is what determines whether you can get out of bed.

The awakening response blunts. Cortisol should rise sharply in the thirty to forty-five minutes after waking. When that spike is absent, mornings are genuinely difficult in a way that has nothing to do with willpower.

Clearance changes. Cortisol is metabolised before excretion, and the rate varies. This produces something that catches people out: two individuals can have identical free cortisol readings, one because they produce a normal amount and clear it normally, the other because they produce a great deal and clear it rapidly. Same number on the page, completely different physiology, completely different intervention.

Receptor sensitivity changes. Cortisol only does anything if receptors respond to it. Sustained high exposure downregulates those receptors, which is why someone can have adequate cortisol and still show the effects of insufficient cortisol signalling.

DHEA declines. The adrenal cortex also produces DHEA, and the relationship between the two is often more informative than either alone.

None of that is a tired gland. All of it is measurable.

Why the distinction is clinical, not pedantic

Because the interventions differ, and one of them is potentially harmful.

If the model is "tired adrenals," the logical response is to stimulate or replace — adrenal glandulars, high-dose licorice, or in the worst cases, low-dose hydrocortisone taken without genuine adrenal insufficiency. Taking exogenous steroid suppresses the very axis you're trying to help. People have been made considerably worse this way.

If the model is dysregulated signalling, the response is different and considerably duller: restore circadian anchoring with morning light, stabilise blood glucose so cortisol isn't being called on overnight to correct it, address the inflammatory or infectious load driving the signal, correct the nutrient cofactors, and manage total demand rather than adding stimulation to a system that's already miscalibrated.

That's less satisfying to sell. It works better.

What I test, and the honest caveat

Dried urine hormone testing over a day gives the free cortisol curve across four or more collections, the metabolised cortisol total, cortisone, DHEA-S, and melatonin. That combination distinguishes high production from fast clearance, which a single reading cannot.

The honest caveat, and I'd rather say it than have you find it elsewhere: the systematic review's criticism of cortisol assessment methodology applies to this field generally. Salivary and dried urine testing are not the diagnostic standard endocrinology uses to diagnose adrenal disease — that's a morning serum cortisol and a synacthen test, and if genuine adrenal insufficiency is on the table, that is the correct pathway and I will refer you for it.

What dried urine testing does well is describe a pattern across a day in someone whose adrenal function is not diseased. That's a different question from "do you have Addison's," and it's the question most people actually have. I use it as a description of how a system is behaving, not as a diagnosis of a condition. Anyone using it as the latter is overreaching.

What to take from this

If a practitioner tells you that you have adrenal fatigue, they're using a label that doesn't survive scrutiny. That should make you ask what else they're saying that they haven't checked.

If a doctor tells you your cortisol is normal and there's nothing wrong, they've answered a narrower question than the one you asked — they've ruled out adrenal disease, which is important and worth doing, but a single morning cortisol says nothing about the shape of your day.

The useful version sits between the two. The gland isn't tired. The regulation is disturbed. That is measurable, it has identifiable drivers, and the drivers are mostly things you can do something about.

Just not by buying something to support your adrenals.

Stephen Duncan is a Functional Diagnostic Nutrition Practitioner (FDN-P, BSc Hons, MSc) based in Edinburgh, working with people since 1988.

Educational content, not medical advice. Persistent fatigue has causes that need a doctor — including anaemia, thyroid disease, diabetes, sleep apnoea and genuine adrenal insufficiency. Get those excluded properly.