Understanding Addison’s Disease in Dogs

Most people do not set out to learn about Addison’s disease. They stumble into it after a run of odd, on and off symptoms that do not quite add up. A dog that seems fine for weeks can suddenly go off their food, vomit, have diarrhoea, or look unusually flat after a small stress, like boarding, a hot day, or a big outing.

It is easy to assume it is a tummy bug, a fussy phase, or “just getting older”. The tricky part is that Addison’s disease can look like lots of other conditions, right up until it becomes urgent. Knowing what it is, and how vets confirm it, helps you act early and avoid a true crisis.^{1, 2}

Understanding Addison’s disease in dogs

Addison’s disease is the everyday name for hypoadrenocorticism, a disorder where the adrenal glands do not produce enough of certain hormones the body relies on for day to day stability.¹

The adrenal glands sit near the kidneys and, among other roles, help the body manage stress, maintain circulation, and keep electrolytes (especially sodium and potassium) in balance. In Addison’s, the key issue is a deficiency of cortisol, and in many dogs, aldosterone as well.^{1, 3}

This is why the condition can look like “everything and nothing”. A dog may show vague gastrointestinal signs, fatigue, or weight loss for a while, then suddenly deteriorate if the body cannot keep blood pressure and electrolytes steady. Some dogs have the so called atypical form, where electrolytes remain normal at first, which can make the pattern even harder to recognise.^{1, 3}

Causes and risk factors

In many dogs, Addison’s disease is thought to be caused by immune mediated damage to the adrenal cortex (the hormone producing part of the adrenal gland). In plain terms, the dog’s immune system appears to target the adrenal tissue over time.^{1, 3}

Less commonly, Addison’s can occur after rapid withdrawal of medications that suppress adrenal function, or due to diseases affecting the pituitary gland (which controls adrenal hormone signalling). These causes are not the majority, but they matter because a dog’s medication history can change how your vet interprets test results.^{1, 3}

You will often see certain breeds mentioned more than others. Guidelines and reviews regularly list breeds such as Standard Poodles and Portuguese Water Dogs among those with increased representation, although Addison’s can occur in any breed.^{1, 3}

Environmental stress does not “cause” Addison’s on its own, but stress can unmask underlying disease. A dog with marginal hormone reserves may cope until a trigger, such as a gastrointestinal illness, surgery, travel, fireworks, or a heatwave, pushes the body beyond what it can compensate for.^{1, 8}

Symptoms you might notice at home

The most common early signs are not dramatic. They tend to be changeable, and they often come and go. Many owners describe their dog as “just not themselves” for a day or two, then seemingly back to normal.

Signs that commonly show up include:

• Reduced appetite and weight loss over time
• Vomiting and or diarrhoea (sometimes intermittently)
• Low energy, weakness, exercise intolerance
• Shaking, discomfort, or a reluctance to move much
• In more severe cases, collapse or signs of shock (pale gums, very weak, cold extremities)

It is also worth knowing that not every dog follows the “classic” pattern. Some dogs have normal sodium and potassium early on, which means routine bloodwork may not point straight to Addison’s. That is one reason vets talk about Addison’s as a “great imitator”.^{1, 8}

If your dog becomes acutely unwell, collapses, or cannot keep water down, treat it as urgent. An Addisonian crisis is a medical emergency, and prompt stabilisation (fluids, electrolyte support, and steroid treatment) can be life saving.⁸

How vets diagnose Addison’s disease

Diagnosis usually starts with the basics: a careful history, physical exam, and standard blood tests. Many dogs with “typical” Addison’s show a characteristic electrolyte pattern, often low sodium and high potassium, alongside dehydration or signs consistent with poor circulation.^{1, 8}

The confirmatory test most commonly used is the ACTH stimulation test. This checks whether the adrenal glands can produce cortisol in response to stimulation. In Addison’s disease, the response is inadequate.^{1, 3}

One practical complication is that some steroids can interfere with cortisol measurement. If a dog needs steroid treatment before testing, vets often choose medications that interfere less with the assay, then plan testing carefully around timing. This is one reason your vet will ask detailed questions about any steroid tablets, creams, ear drops, or injections your dog has received.^{4, 7}

Because atypical cases may not show the “textbook” electrolytes, vets sometimes pursue Addison’s testing when a dog has recurring gastrointestinal signs, unexplained weakness, or bloodwork changes that suggest cortisol deficiency, even if sodium and potassium look normal.^{1, 8}

Treatment and long term management

Treatment is about replacing what the body cannot reliably make. Most dogs need lifelong hormone replacement, and once stable, many return to a normal routine with only modest day to day adjustments.^{3, 8}

Replacement usually includes:

• Glucocorticoids (often prednisone or prednisolone) to replace cortisol.
• Mineralocorticoids to replace aldosterone in dogs with electrolyte abnormalities, commonly desoxycorticosterone pivalate (DOCP) injections, or sometimes fludrocortisone tablets.^{2, 3, 6}

Dosing is individual. Vets adjust medications based on the dog’s clinical signs, side effects (such as increased thirst and urination), and follow up bloodwork, especially sodium and potassium monitoring for mineralocorticoid therapy. With DOCP, electrolytes are typically checked after starting or changing the dose, then at intervals once stable.^{2, 6}

Many dogs also need extra glucocorticoid around stress. That might mean temporarily increasing the steroid dose for events like surgery, travel, kennel stays, or significant illness. Your vet will guide you on what “stress dosing” means for your dog, and when it is appropriate.^{2, 3}

Living well with an Addisonian dog

Once your dog is stable, life usually becomes pleasantly ordinary again. The steadying factors are routine, observation, and a good relationship with your veterinary team.

Things that tend to help in practice:

• Keep medication consistent, and do not stop steroids suddenly unless your vet instructs it.
• Make follow up blood tests part of the rhythm, especially early on when doses are being fine tuned.
• Be cautious with big changes, like a sudden increase in exercise intensity, hot weather exertion, or travel. You do not need to avoid these forever, but gradual change is kinder on a body that relies on replacement hormones.
• Know your dog’s early warning signs, which might be as simple as quieter behaviour, skipping breakfast, or mild vomiting, and check in with your vet earlier rather than later.

If your dog has a vomiting episode, diarrhoea, or seems unusually weak, it is reasonable to treat that as meaningful. Not every unwell day is Addison’s related, but because cortisol is part of how dogs cope with illness, small problems can escalate faster if hormone support is insufficient.⁸

Prognosis and lifespan

The outlook for dogs with Addison’s disease is generally excellent with treatment. Dogs that are diagnosed and stabilised typically do well long term, and many die of unrelated causes later in life rather than from Addison’s itself.⁸

Prognosis depends less on breed or age and more on practical details, such as how quickly the condition is recognised, whether a dog has had a severe crisis, and how reliably treatment and monitoring can be maintained. The early period after diagnosis can involve several dose adjustments, but it usually settles into a manageable pattern.^{2, 3, 8}

For many owners, the hardest part is accepting that the symptoms were real even when they were inconsistent. If your dog has been diagnosed, it can help to reframe the condition as a problem of regulation rather than fragility. With the right support, most Addisonian dogs can still enjoy walks, play, training, and family life, just with a bit more planning behind the scenes.

References

1. AAHA: Canine hypoadrenocorticism (Addison’s disease) (2023 guidelines)
2. AAHA: Canine hypoadrenocorticism therapy (2023 guidelines)
3. PubMed: Management of hypoadrenocorticism (Addison’s disease) in dogs
4. Veterinary Medicine: Research and Reports: Management of hypoadrenocorticism (Addison’s disease) in dogs
5. PubMed: Low-dose ACTH stimulation testing in dogs suspected of hypoadrenocorticism
6. Today’s Veterinary Practice: Diagnosis and management of hypoadrenocorticism in dogs
7. Michigan State University Veterinary Diagnostic Laboratory: Adrenal testing in dogs
8. Veterinary Specialist Services (Australia): Treatment of hypoadrenocorticism