What Is Addison's Disease in Dogs? (Hypoadrenocorticism)

An Addisonian crisis is a medical emergency. If your dog collapses, cannot stand, is profoundly weak, is vomiting repeatedly, has a slow or irregular heartbeat, has pale gums or seems to be going into shock, go to an emergency vet immediately and say that Addison's disease is suspected or confirmed. Outside of a crisis, call your regular veterinarian promptly if your dog has repeated unexplained episodes of lethargy, vomiting, diarrhoea, weakness, shivering or weight loss, especially if those episodes follow stressful events and improve with fluids, and ask directly whether adrenal testing is appropriate.

Addison's disease in dogs, known in veterinary medicine as hypoadrenocorticism, is a condition in which the adrenal glands stop producing enough of two essential hormone groups: glucocorticoids (mainly cortisol) and, in most cases, mineralocorticoids (mainly aldosterone). Cortisol governs how a dog handles physical and emotional stress, how it mobilises blood sugar, and how it maintains blood pressure and gut lining integrity. Aldosterone tells the kidneys how much sodium to hold onto and how much potassium to excrete. When those hormones run short, a dog loses the ability to buffer ordinary stress, and the illness that follows can imitate almost anything.

So yes, dogs can get Addison's disease. It is considered uncommon compared with endocrine conditions such as hypothyroidism, but it is well described in standard veterinary references, including the Merck Veterinary Manual and the Veterinary Partner library maintained by the Veterinary Information Network. It is also one of the more recognisable diagnoses in internal medicine once it is finally on the table, because the testing is clear-cut and the treatment is straightforward for a veterinarian to supervise.

The great pretender: why the signs are so easy to miss

Addison's is nicknamed 'the great pretender' for a reason. The early picture is a collection of vague, waxing and waning complaints: lethargy, poor appetite, intermittent vomiting or diarrhoea, gradual weight loss, muscle weakness, shivering, increased thirst and urination. The dog looks unwell for a few days, maybe gets fluids and an anti-nausea injection at the clinic, bounces back, and everyone assumes it was a bad bout of gastroenteritis. Weeks or months later it happens again.

That pattern of repeated, unexplained crashes that improve with supportive care is the thread owners most often recognise in hindsight, and it is the same story that repeats in owner discussion threads on Reddit and in breed group forums. The episodes frequently follow stress: boarding, travel, a thunderstorm, a change in household routine, a minor surgery. A healthy dog meets stress with a surge of cortisol. A dog with failing adrenal glands cannot produce that surge.

The emergency presentation is called an Addisonian crisis. Sodium falls, potassium climbs, blood volume drops, and the dog can collapse with a slow heart rate, severe dehydration and shock. This is a genuine veterinary emergency that needs intravenous fluids and hospital care immediately. If your dog has had more than one unexplained bout of weakness and gastrointestinal upset, especially around a stressful event, that history alone is worth raising with your veterinarian and asking directly whether adrenal testing is appropriate.

Typical, atypical, secondary and iatrogenic: the forms explained

Not all hypoadrenocorticism looks the same on bloodwork, which is a large part of why it gets missed. The forms differ by which hormones are deficient and why.

Form	What is deficient	Electrolytes	Usual cause
Primary (typical)	Cortisol and aldosterone	Low sodium, high potassium, low sodium:potassium ratio	Immune-mediated destruction of the adrenal cortex
Primary atypical	Cortisol only, at least initially	Normal, which is why it is so easily overlooked	Partial adrenal cortex damage; some dogs later progress to the typical form
Secondary	Cortisol only	Normal	Insufficient ACTH signalling from the pituitary gland; uncommon
Iatrogenic	Cortisol, sometimes aldosterone	Variable	Abrupt withdrawal of long-term steroid treatment, or an effect of certain medications used to manage Cushing's disease

The atypical form matters enormously in practice. A dog can be genuinely cortisol deficient and still show a textbook-normal sodium and potassium panel, so the usual electrolyte red flag never appears. Those dogs often carry a working diagnosis of chronic gastrointestinal disease, a food sensitivity, or simply a sensitive stomach for a long time before the adrenal axis is tested.

Iatrogenic cases are the one form with an element of prevention attached. Steroids given over an extended period suppress the body's own cortisol production, and stopping them abruptly removes the supply before the glands have resumed their own. This is exactly why veterinarians taper steroid treatment rather than stopping it outright, and why no one should discontinue a prescribed medication without the prescribing veterinarian's direction.

What causes it, and whether it is hereditary

In the great majority of dogs, primary Addison's is immune-mediated: the immune system gradually destroys the hormone-producing layers of the adrenal cortex. Signs do not usually appear until a substantial proportion of that tissue is gone, which is why the onset can feel abrupt even though the underlying process has been building quietly. Far less commonly, the adrenal cortex is damaged by infiltrative disease, haemorrhage or infarction, or by the medications mentioned above.

Owners often ask how their dog got it, usually with a note of guilt. The honest answer is that nothing you fed, missed or did wrong caused this. It is not contagious, not a consequence of diet, exercise or vaccination, and not something you could have spotted earlier through more attentive care. It is an internal immune process.

There is a clear hereditary component in several breeds. Familial patterns have been documented in Standard Poodles, Portuguese Water Dogs, Bearded Collies and Nova Scotia Duck Tolling Retrievers, with an inherited mode of transmission described in breeding studies for some of those lines. Increased risk is also reported in Great Danes, Rottweilers, West Highland White Terriers, Soft Coated Wheaten Terriers and Leonbergers, among others. Mixed-breed dogs get it too, so breed is a risk signal, not a filter.

As for age of onset, Addison's is most often diagnosed in young to middle-aged adult dogs, which is unusual among endocrine diseases and part of why it surprises people. Female dogs have historically been reported as over-represented, although that pattern is not absolute and does not hold equally across all breeds. A senior dog can still be diagnosed, and a dog under two years old can be too.

Diagnosis, lifelong management and what the outlook looks like

Diagnosis starts with a standard chemistry panel and complete blood count, where a veterinarian may notice low sodium, high potassium, a low sodium:potassium ratio, elevated kidney values, low blood sugar or an unexpectedly unremarkable white cell pattern in a sick dog. A baseline cortisol measurement is a useful screening step; a resting cortisol above a certain threshold effectively rules the disease out. Confirmation comes from an ACTH stimulation test, which measures whether the adrenal glands can respond to a stimulating hormone at all. In a dog with Addison's, they cannot.

Treatment is usually lifelong treatment your vet prescribes, replacing what the adrenal glands can no longer make. Your vet may prescribe medication given on a repeating schedule, sometimes by injection and sometimes by mouth, and may advise adjusting the plan temporarily around stressful events. Every detail of that plan, including what is given, how often, and how it changes over time, is set and revised by your veterinarian using follow-up examinations and electrolyte checks. Never change, pause or stop a prescribed medication on your own.

Management is a vet-led routine rather than a dramatic one. Expect regular recheck appointments, repeat bloodwork to see how electrolytes and kidney values are tracking, and conversations about how your dog is doing between visits. Many dogs settle into a stable rhythm and live normal, active lives, although results vary from dog to dog, and some need more frequent adjustment early on than others. The ongoing work is practical: giving medication exactly as directed, keeping to recheck appointments, flagging stressful events in advance, and knowing the warning signs of a crisis.

What to watch at home, and what to tell your vet

Before a diagnosis, the single most useful thing an owner can do is keep a plain written record. Note the date of each episode, how long it lasted, what happened just before it (boarding, a storm, travel, a vet visit, a change in routine), and what the dog looked like: appetite, energy, vomiting or diarrhoea and how often, water intake, how often they asked to go out, any shivering or trembling, any wobbliness, and how quickly they returned to normal. Weigh your dog when you can and write the number down, because slow weight loss is easy to miss at home. Short phone videos of weakness, trembling or an unsteady walk are often more informative to a veterinarian than a description after the fact.

Bring that record to the appointment along with copies of previous bloodwork and discharge notes from any emergency visits, plus a complete list of everything your dog receives, including anything given over the counter and any steroid course given recently or in the past. If your dog has been stable and then slips, say so plainly, and ask whether adrenal testing fits the picture.

After a diagnosis, the home job is consistency and observation. Keep a simple log of when medication is given and when the next recheck is due, and tell your vet in advance about anything stressful on the calendar so they can advise ahead of time. Contact your veterinarian promptly if your dog seems flat for more than a day, goes off food, vomits or has diarrhoea, drinks noticeably more or less than usual, trembles, tires quickly on normal walks, or cannot keep a dose of medication down.

Treat it as an emergency, and go straight to emergency care, if your dog collapses or cannot rise, is extremely weak or disoriented, has pale or grey gums, feels cold at the ears and paws, has a slow or irregular heartbeat, vomits repeatedly or vomits blood, passes black or bloody stool, or becomes unresponsive. Call ahead so the hospital knows an Addisonian crisis is possible, and bring the medication list with you.

Key Takeaways

• Addison's disease, or hypoadrenocorticism, means the adrenal glands are not producing enough cortisol and usually not enough aldosterone.
• It is called the great pretender because its signs, lethargy, vomiting, weakness and weight loss, come and go and mimic many other illnesses.
• The main forms are primary typical, primary atypical with normal electrolytes, secondary from pituitary signalling failure, and iatrogenic from steroid withdrawal or Cushing's medication.
• Most cases are immune-mediated, and there is a documented hereditary component in Standard Poodles, Portuguese Water Dogs, Bearded Collies and Nova Scotia Duck Tolling Retrievers.
• It is most often diagnosed in young to middle-aged adult dogs, and nothing an owner did caused it.
• Diagnosis rests on bloodwork plus an ACTH stimulation test; treatment is usually lifelong treatment your vet prescribes, and results vary from dog to dog.
• An Addisonian crisis is an emergency; collapse, severe weakness and a slow heart rate need immediate veterinary attention.

Your veterinarian owns the diagnosis here, and owns the treatment plan. The ACTH stimulation test, the medication plan, the adjustments after each recheck and the instructions for stressful periods are all theirs to set and revise. Your part is steady observation at home, clear notes to hand over at each visit, and fast action when something looks wrong.

Nothing in this article treats, cures or prevents any condition; every decision about your dog's care belongs with your veterinarian.

Related guides: Senior Dog Bloodwork : What a Senior Blood Panel Shows and Signs of a Dog With Thyroid Problems : What to Look For.