Health condition · Clinically reviewed
Adrenal insufficiency, a rare but life-threatening condition to know.
Insufficient cortisol production — from adrenal disease (Addison’s) or pituitary failure. Diagnosis is blood tests plus a Synacthen test; treatment is lifelong replacement and sick-day rules.
Why trust this guide
- 01
Clinically reviewed
Written by our editorial team and reviewed by a registered UK clinician before publication.
- 02
Sourced from guidance
Every claim is checked against Society for Endocrinology, NHS and Endocrine Society sources you can see at the end.
- 03
Current for 2026
Reflects UK guidance on Synacthen testing, replacement therapy and the NHS steroid emergency card.
Key facts
Adrenal insufficiency at a glance.
The essentials, in plain English — what it is, why it is dangerous, how it is diagnosed, and how it is safely treated in the UK today.
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What it is
Insufficient cortisol production — primary (adrenal, e.g. Addison’s), secondary (pituitary ACTH failure), or tertiary (hypothalamic).
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Addison’s disease
Primary autoimmune adrenal failure — the immune system destroys adrenal cortex tissue.
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Most common cause
Long-term glucocorticoid therapy is the commonest cause of secondary adrenal insufficiency worldwide.
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Adrenal crisis
A medical emergency — collapse, vomiting and hypotension needing immediate IM hydrocortisone and 999.
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Diagnosis
The short Synacthen test is the standard diagnostic — cortisol response to synthetic ACTH.
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Sick-day rules
Life-saving — always carry a steroid emergency card and an IM hydrocortisone kit.
Why this guide matters
A rare diagnosis, an emergency you never forget.
Adrenal insufficiency is uncommon, easy to miss and lethal in crisis — but very manageable once recognised. Three points shape the rest of this guide.
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A blood test and Synacthen settle it
Cortisol, ACTH and the short Synacthen test are decisive.
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Sick-day rules save lives
Doubling doses and the IM emergency kit prevent crisis.
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The card is non-negotiable
Every patient carries an NHS steroid emergency card.
How the diagnosis is made
From first symptom to safe replacement.
The seven steps a UK team will normally follow, in order — so you know what to expect and why.
Phase 1 · Recognising
Symptoms, steroid history and 9am cortisol
Phase 2 · Confirming
Synacthen, antibodies and pituitary imaging
Phase 3 · Managing
Endocrinology, replacement and the emergency kit
- 01
Recognising
Symptoms and steroid history
Chronic fatigue, dizziness, weight loss, pigmentation — plus any long-term steroid use, pituitary surgery or radiotherapy.
- 02
Recognising
9am cortisol
A morning cortisol under 100 nmol/L strongly suggests AI; over 400 nmol/L makes it unlikely.
- 03
Recognising
ACTH level
High ACTH points to primary (adrenal) disease; low or normal ACTH points to secondary (pituitary) failure.
- 04
Confirming
Short Synacthen test
Synthetic ACTH given; cortisol measured at 0 and 30 minutes — a peak below 420-500 nmol/L confirms AI.
- 05
Confirming
Adrenal autoantibodies
21-hydroxylase antibodies confirm autoimmune Addison’s disease.
- 06
Confirming
MRI pituitary
Imaging the pituitary if secondary AI is suspected — to identify tumour, infarction or infiltration.
- 07
Managing
Endocrinology consultation
Specialist review to start replacement, teach sick-day rules and arrange the emergency kit.
Typical pathway: a few weeks from first blood test to a confirmed diagnosis and emergency kit in hand.
Symptoms
What adrenal insufficiency actually feels like.
Symptoms come on slowly and overlap with everyday illness — which is why the diagnosis is often missed until a crisis reveals it.
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Chronic fatigue
Deep, persistent tiredness that rest does not fix — often the earliest symptom.
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Dizziness on standing
Postural hypotension from mineralocorticoid deficiency in primary AI.
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Weight loss
Unintentional weight loss with loss of appetite over weeks to months.
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Skin hyperpigmentation
Darkening of palmar creases, scars, buccal mucosa — classic in primary Addison’s disease.
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GI symptoms
Nausea, abdominal pain, vomiting and diarrhoea — commonly misattributed to gastroenteritis.
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Salt craving
A distinctive craving for salty foods in primary AI due to aldosterone deficiency.
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Poor recovery from illness
Minor infections or stresses cause disproportionate collapse — a warning sign of unrecognised AI.
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Red flag: adrenal crisis
Vomiting, hypotension, collapse — 999 with IM hydrocortisone. Do not wait for tests.
Treatment
How adrenal insufficiency is treated in the UK.
Lifelong hormone replacement, sick-day rules and an emergency kit. Here is what each part of the plan does — and why the details matter.
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Hydrocortisone replacement
Physiological glucocorticoid replacement — typically 15-25 mg daily split into 2-3 doses to mimic diurnal rhythm.
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Fludrocortisone (primary AI)
Mineralocorticoid replacement for primary AI — usually 50-200 mcg once daily to control sodium, potassium and blood pressure.
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Sick-day doubling
Double the oral hydrocortisone dose during fever, infection or minor illness until recovery.
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IM hydrocortisone emergency kit
100 mg hydrocortisone for self- or partner-injection during vomiting, trauma or collapse — before calling 999.
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Steroid emergency card
NHS-issued red card carried at all times — alerts clinicians to the need for stress-dose steroids.
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Medical alert jewellery
A wearable bracelet or tag identifying adrenal insufficiency for use if unconscious.
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Endocrinology follow-up
Annual review of replacement dose, sick-day competence, cardiovascular risk and comorbid autoimmune disease.
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Bone-density surveillance
DEXA every few years on long-term steroids — over-replacement drives osteoporosis risk.
What this guide is based on
The sources behind every number on this page.
UK national guidance and specialist society standards, current at the time of last review.
Key references
Guidelines and standards we relied on.
A quiet reminder
This guide is for information, not medical advice.
Your endocrinologist knows your history and can tell you which parts apply to you. Never stop steroid replacement without specialist review.
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Society for Endocrinology. Clinical guidance on adrenal insufficiency.
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NHS. Emergency steroid card guidance (2020).
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Endocrine Society. Clinical practice guidelines on adrenal insufficiency.
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Addison’s Disease Self-Help Group. Patient information.
Red flags
When adrenal insufficiency becomes an emergency.
Adrenal insufficiency is stable when replaced correctly. These are the situations where it stops being routine — and you should act promptly.
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Adrenal crisis
Vomiting, hypotension, collapse — 999, IM hydrocortisone, IV fluids. Time-critical.
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AI plus gastroenteritis
Vomiting stops oral absorption — use the IM emergency kit and seek urgent care.
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Surgery without steroid cover
Any operation or major dental work needs stress-dose IV hydrocortisone — never omit.
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Pregnancy without adjusted doses
Hydrocortisone requirement rises in the third trimester and needs stress cover for labour.
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Missed doses
Even a single missed dose can precipitate crisis — take as soon as remembered.
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Skin colour change post-op
New pigmentation change after pituitary or adrenal surgery — review urgently.
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Post-pituitary surgery
ACTH deficiency may be immediate or delayed — never stop steroids without endocrine review.
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Radiotherapy-related AI
Cranial or adrenal radiotherapy causes late AI — arrange periodic axis testing.
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New symptomatic hypoglycaemia
Unexplained low glucose in a steroid-treated patient — consider inadequate replacement.
Living with it
A lifelong condition, a very manageable one.
Four small things that make the biggest difference day to day — routine, preparedness, sick-day discipline and yearly reviews.
A quiet reminder
Preparation prevents crisis.
Carry the card, carry the kit, and never skip a dose — the difference between a rough day and a hospital admission.
- 01 Routine
Own your daily doses
Take hydrocortisone at consistent times — waking, midday, mid-afternoon — to mirror natural cortisol.
- 02 Preparedness
Carry the card and the kit
Steroid emergency card and IM hydrocortisone within reach at all times, including holidays.
- 03 Sick days
Double when unwell, inject when sick
Fever or infection: double the dose. Vomiting or collapse: inject and call 999.
- 04 Reviews
Annual endocrine review
Yearly check of dose, bone density, cardiovascular risk and sick-day competence.
Frequently asked
Everything we get asked about adrenal insufficiency.
Quick answers on primary vs secondary AI, Synacthen testing, sick-day rules, the emergency card and when to worry.
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What is the difference between Addison’s and secondary adrenal insufficiency?
Addison’s (primary AI) is adrenal failure — usually autoimmune — with high ACTH, low cortisol and often low aldosterone. Secondary AI is pituitary ACTH deficiency: cortisol is low, ACTH is low or normal, and aldosterone is preserved.
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How is adrenal insufficiency diagnosed?
A 9am cortisol and ACTH plus the short Synacthen test — measuring cortisol response 30 minutes after synthetic ACTH. A subnormal peak confirms the diagnosis.
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What are sick-day rules?
Double the oral hydrocortisone dose for fever or infection, and use the IM hydrocortisone emergency kit for vomiting, trauma or collapse — then attend hospital.
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Why do I need a steroid emergency card?
It tells clinicians you cannot make your own cortisol and need stress-dose steroids in any emergency, surgery or serious illness.
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Can adrenal insufficiency be caused by steroid tablets?
Yes — long-term glucocorticoids suppress the HPA axis and are the commonest cause of secondary AI. Never stop long-term steroids abruptly.
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When should I go to A&E?
Vomiting that stops you keeping medication down, collapse, severe dizziness, or any symptoms of adrenal crisis — call 999 and use your IM hydrocortisone kit first.
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