CONDITION

Addisons Disease in Dogs

A hormonal condition where the adrenal glands produce insufficient cortisol and aldosterone, causing episodic weakness and metabolic disruption.

Why this matters now

Addison's disease (hypoadrenocorticism) can affect dogs of any age but is most commonly diagnosed in young to middle-aged dogs, typically between two and seven years. Certain breeds, including Standard Poodles, Portuguese Water Dogs, Bearded Collies, and Nova Scotia Duck Tolling Retrievers, appear to have a higher predisposition. The condition can be challenging to identify initially because its signs are often vague and intermittent, resembling many other conditions.

The course of Addison's disease varies considerably depending on how and when it is identified. Some dogs present with a gradual decline in energy and appetite over weeks to months, with signs that wax and wane. Others may first come to attention during an acute crisis when the adrenal glands can no longer maintain adequate hormone levels. Once identified and appropriately managed, many dogs can maintain a good quality of life for years, though the condition requires ongoing monitoring and lifelong hormone replacement.

Signals & patterns

Early signals

Episodic lethargy and weakness

Dogs may experience intermittent periods of unusual tiredness or weakness that resolve on their own, only to return days or weeks later. These episodes can be triggered by stress, excitement, or changes in routine. Because they are self-limiting, owners often attribute them to the dog having an off day. The episodic, waxing-and-waning nature of this pattern is one of the hallmarks that distinguishes early Addison's disease from many other conditions.

Reduced appetite with intermittent vomiting

Appetite may fluctuate, with the dog eating normally for periods and then showing reduced interest in food. Occasional vomiting or nausea may accompany these episodes. The gastrointestinal signs can be mild and self-resolving, which often leads to investigation of dietary sensitivities or gastrointestinal conditions before Addison's disease is considered. Some dogs develop a pattern of appetite changes that coincide with stressful events.

Increased water intake and urination

As the kidneys lose sodium due to aldosterone deficiency, the body compensates by increasing fluid intake to maintain blood volume. This polydipsia and polyuria may be subtle initially and can overlap with many other conditions. The degree of increased drinking may fluctuate in parallel with the episodic nature of the disease, being more pronounced during periods of adrenal insufficiency.

Intermittent muscle trembling or shaking

Mild trembling, particularly after exercise or during stressful situations, may be observed. This can relate to electrolyte imbalances, particularly elevated potassium levels, which affect muscle and nerve function. The trembling may be brief and easily dismissed as cold sensitivity or excitement. In some dogs, this manifests as a general sense of unsteadiness rather than visible shaking.

Later signals

Collapse or profound weakness

During an Addisonian crisis, dogs may collapse, become profoundly weak, or show signs of shock including a weak pulse, pale gums, and low body temperature. This represents a failure of the adrenal glands to produce sufficient hormones to maintain cardiovascular function. A crisis can develop rapidly, sometimes within hours, and is often triggered by a stressful event such as boarding, travel, surgery, or illness. Some dogs are first diagnosed during a crisis, with the earlier subtle signs having gone unrecognised.

Severe dehydration despite adequate water intake

Without sufficient aldosterone, the kidneys cannot retain sodium effectively, leading to progressive fluid loss. Dogs may appear dehydrated with sunken eyes, tacky gums, and reduced skin elasticity even when they have been drinking normally. This dehydration reflects the underlying electrolyte imbalance rather than inadequate fluid intake and does not resolve simply by offering more water.

Slow heart rate (bradycardia)

Elevated potassium levels can directly affect cardiac conduction, leading to a slower than expected heart rate. This is particularly significant because most conditions that cause weakness, dehydration, and low blood pressure would be expected to produce a compensatory increase in heart rate. The combination of low blood pressure with a normal or slow heart rate is a distinctive finding that often prompts investigation for Addison's disease.

Persistent gastrointestinal disturbance

Chronic or recurrent vomiting, diarrhoea, and weight loss may become more prominent as the disease progresses. Some dogs develop bloody diarrhoea or abdominal pain. The gastrointestinal involvement can be severe enough to mimic inflammatory bowel disease, pancreatitis, or other primary gastrointestinal conditions, earning Addison's disease the nickname 'the great pretender' in veterinary medicine.

Click to read about the biological mechanisms

How this is usually investigated

Investigating Addison's disease involves a combination of blood work, electrolyte analysis, and specific hormone testing. Because the condition can mimic many other diseases, it is sometimes identified after other conditions have been ruled out, though certain blood work patterns can raise suspicion early in the diagnostic process.

Routine blood work and electrolytes

Purpose: A complete blood count and biochemistry panel can reveal several suggestive patterns. The classic finding is a sodium-to-potassium ratio below 27:1, reflecting sodium loss and potassium retention due to aldosterone deficiency. Other findings may include elevated kidney values (pre-renal azotaemia from dehydration), low blood glucose, mild anaemia, and the absence of a stress leucogram (a white blood cell pattern normally expected in unwell dogs).
Considerations: Not all dogs with Addison's disease show the classic electrolyte changes. In atypical Addison's disease, aldosterone production may be partially preserved while cortisol is deficient, resulting in normal electrolytes. The absence of electrolyte abnormalities does not exclude the diagnosis. Kidney values may normalise with fluid therapy, which can confuse the picture if Addison's disease is not considered.

ACTH stimulation test

Purpose: This is the definitive test for Addison's disease. A baseline cortisol sample is taken, synthetic ACTH (cosyntropin) is administered to stimulate the adrenal glands, and a second cortisol sample is collected one hour later. In healthy dogs, cortisol rises significantly in response to ACTH stimulation. In dogs with Addison's disease, both baseline and post-stimulation cortisol levels remain low, indicating that the adrenal glands lack the capacity to produce cortisol even when directly stimulated.
Considerations: Certain medications, particularly corticosteroids, can interfere with the test results. Dogs that have recently received steroid treatment may show suppressed cortisol levels that mimic Addison's disease. Ideally, corticosteroids should be withheld before testing, though dexamethasone is sometimes used as an interim treatment because it does not cross-react with most cortisol assays.

Baseline cortisol measurement

Purpose: A resting cortisol level can serve as a screening test. A baseline cortisol above a certain threshold makes Addison's disease very unlikely, potentially avoiding the need for the more involved ACTH stimulation test. However, a low baseline cortisol is not diagnostic on its own and requires confirmation with the stimulation test.
Considerations: Stress, illness, and certain medications can all influence baseline cortisol levels. The value of this test lies primarily in its ability to rule out Addison's disease when the result is above the threshold. A single normal result during a well period does not exclude the possibility of intermittent adrenal insufficiency.

Electrocardiography (ECG)

Purpose: An ECG can detect cardiac conduction abnormalities caused by elevated potassium levels. Characteristic changes include peaked T waves, prolonged PR intervals, widened QRS complexes, and in severe cases, atrial standstill. These findings, combined with bradycardia, provide supportive evidence for hyperkalaemia and can guide the urgency of treatment.
Considerations: ECG changes correlate broadly but not perfectly with potassium levels. Some dogs tolerate relatively high potassium levels without dramatic ECG changes, while others show significant conduction disturbances at moderately elevated levels. The ECG provides a real-time assessment of cardiac risk that serum potassium values alone may not fully reflect.

Options & trade-offs

Management of Addison's disease involves replacing the hormones that the adrenal glands can no longer produce. The approach typically combines mineralocorticoid replacement to restore electrolyte balance with glucocorticoid supplementation for cortisol deficiency. The specifics of management often evolve as the individual dog's requirements become clearer over time.

Injectable mineralocorticoid replacement (DOCP)

Desoxycorticosterone pivalate (DOCP) is administered as an intramuscular injection, typically every 25-28 days, to replace aldosterone function. This approach provides consistent mineralocorticoid replacement with predictable blood levels. The dose is adjusted based on electrolyte monitoring, with the interval between injections sometimes being extended once stable levels are achieved.

Trade-offs: DOCP requires regular veterinary visits for injection and monitoring blood work. The initial period of dose adjustment may involve more frequent visits and blood tests. The injectable route ensures compliance but means the dog is dependent on access to veterinary care at regular intervals. DOCP does not provide glucocorticoid activity, so oral prednisolone or prednisone must also be given.

Oral mineralocorticoid replacement (fludrocortisone)

Fludrocortisone is an oral tablet given daily that provides both mineralocorticoid and some glucocorticoid activity. This allows owners to manage the condition at home with daily dosing. The dose is adjusted based on periodic electrolyte monitoring until a stable regimen is established.

Trade-offs: Daily oral medication requires consistent owner compliance. The dose may need to increase over time as the remaining adrenal tissue continues to deteriorate. Fludrocortisone can cause increased thirst and urination at higher doses. Some dogs require additional glucocorticoid supplementation despite fludrocortisone's partial glucocorticoid activity. The cost of fludrocortisone can be significant, particularly for larger dogs.

Glucocorticoid supplementation

Oral prednisolone or prednisone is given daily at physiological replacement doses to compensate for cortisol deficiency. The dose is typically kept as low as possible to avoid the side effects associated with higher glucocorticoid doses. During periods of anticipated stress, such as travel, boarding, or illness, the dose may be temporarily increased to mimic the normal cortisol surge that a healthy adrenal gland would produce.

Trade-offs: Finding the optimal daily dose requires balancing adequate cortisol replacement against the side effects of excess glucocorticoids, which can include increased thirst, urination, appetite, and over time, potential metabolic effects. Stress dosing requires owners to anticipate and respond to stressful situations, which involves judgement about what constitutes sufficient stress to warrant a dose increase.

Electrolyte and clinical monitoring

Regular blood work to monitor sodium, potassium, kidney values, and general health parameters is an integral part of managing Addison's disease. Monitoring frequency is typically higher during the initial dose adjustment period and may reduce to every three to six months once stable. Clinical monitoring includes tracking body weight, appetite, energy levels, and any recurrence of symptoms.

Trade-offs: Ongoing monitoring involves regular veterinary visits and associated costs. The frequency of monitoring needs to be balanced against the stability of the condition and the practical impact on the owner. Under-monitoring risks missing electrolyte imbalances before they become clinically significant, while over-monitoring adds unnecessary cost and disruption.

Common misconceptions

Misconception:

"Addison's disease is always obvious and dramatic in its presentation"

Reality:

The condition is frequently referred to as 'the great pretender' because its signs can be remarkably subtle and non-specific. Many dogs experience months of intermittent, vague symptoms including occasional lethargy, appetite changes, and mild gastrointestinal upset before the condition is identified. The episodic nature, where dogs can appear completely normal between episodes, often delays recognition. While an Addisonian crisis can be dramatic, this represents the extreme end of a spectrum that often begins with very mild, easily overlooked changes.

Misconception:

"Once diagnosed, Addison's disease is difficult to manage and severely limits quality of life"

Reality:

With appropriate hormone replacement, many dogs with Addison's disease lead full, active lives with a normal or near-normal life expectancy. The condition does require lifelong management and regular monitoring, but once a stable medication regimen is established, many owners report that the day-to-day impact is minimal. The key consideration is the need for consistent medication and the ability to recognise and respond to situations that may require temporary dose adjustments.

Misconception:

"Normal electrolyte results rule out Addison's disease"

Reality:

While the classic presentation of Addison's disease includes sodium and potassium imbalances, a subset of dogs develop 'atypical' Addison's disease where cortisol production is deficient but aldosterone production remains partially intact. These dogs can present with normal electrolytes, making the diagnosis more challenging. Atypical cases may eventually progress to typical Addison's disease as the remaining adrenal tissue deteriorates, but the initial presentation with normal electrolytes can lead to delayed diagnosis.

Understanding the patterns of Addison's disease in an individual dog often develops over time through observation and monitoring. The condition's episodic nature means that recognising triggers and early warning signs can become clearer with experience. Many dogs with well-managed Addison's disease live full, active lives, and the approach to management may be refined as the individual dog's needs become better understood.

Last reviewed: 24 April 2026 · Dr Alastair Greenway MRCVS