CONDITION
Addisons Disease in Dogs
A hormonal condition where the adrenal glands produce too little cortisol and often aldosterone, causing episodic weakness and illness and, in some dogs, a crisis that can progress to collapse within hours and be fatal without treatment.
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 first come to attention during an acute crisis, often after a stressful event, in which dehydration, low blood pressure, low blood sugar and a rising potassium level can progress to collapse and a dangerously slow or irregular heartbeat over hours rather than days, and without treatment a crisis can be fatal. 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, chronic sodium wasting washes out the normal renal medullary concentration gradient, leaving the kidneys unable to concentrate urine even as the dog becomes volume-depleted. This produces polyuria, and the dog then drinks more (polydipsia) to compensate for this ongoing obligate water loss; the pattern 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 may relate to muscle weakness, electrolyte imbalance or low blood sugar. 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 on examination, although not every dog in crisis shows it, and heart rate and rhythm in a weak or collapsed dog cannot be reliably judged at home.
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.
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
ACTH stimulation test
Baseline cortisol measurement
Electrocardiography (ECG)
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)
Desoxycortone pivalate (DOCP), licensed in the UK as Zycortal, is given by injection under the skin, typically at intervals of around a month, 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 daily oral prednisolone is usually given alongside it. A delayed injection can allow potassium to rise and sodium to fall, and this can lead to a crisis.
Oral mineralocorticoid replacement (fludrocortisone)
Fludrocortisone is an oral tablet given once or twice 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. In the UK, fludrocortisone is a human medicine that is not licensed for dogs, so it is prescribed under the veterinary medicines cascade. Missed tablets, or vomiting that prevents absorption, can allow electrolyte levels to shift within days.
Glucocorticoid supplementation
Oral prednisolone is given daily at physiological replacement doses to compensate for cortisol deficiency. Prednisolone tablets are authorised for dogs in the UK for inflammatory, allergic and immune-mediated conditions, so using them as hormone replacement is off-licence, under the veterinary medicines cascade. The Zycortal datasheet itself names prednisolone as a glucocorticoid to give alongside it. 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 right 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 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
"Addison's disease is always obvious and dramatic in its presentation"
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.
"Once diagnosed, Addison's disease is difficult to manage and severely limits quality of life"
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 main consideration is the need for consistent medication and the ability to recognise and respond to situations that may require temporary dose adjustments.
"Normal electrolyte results rule out Addison's disease"
While the classic presentation of Addison's disease includes sodium and potassium imbalances, a subset of dogs develop 'atypical' Addison's disease where cortisol is deficient but sodium and potassium stay normal, in some dogs because aldosterone is still partly produced. The normal electrolytes make 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.
Related conditions
Cushings Disease in Dogs
Cushing's disease represents the opposite hormonal pattern to Addison's disease (excess cortisol rather than deficiency), and distinguishing between the two often relies on contrasting clinical pictures and laboratory findings. Dogs treated for Cushing's disease can develop hypoadrenocorticism if the medication suppresses the adrenal glands too far. This is a recognised complication of treatment: in one study of 156 dogs given trilostane, an estimated 15% developed it within two years, and in most affected dogs it was temporary.
Hypothyroidism in Dogs
Hypothyroidism and Addison's disease can both present with lethargy, reduced exercise tolerance and weight change, and may occasionally coexist as part of a broader autoimmune process affecting multiple endocrine glands. Distinguishing the two typically requires specific hormone testing, as the clinical overlap can be substantial.
Chronic Kidney Disease in Dogs
Chronic kidney disease can mimic some of the metabolic and electrolyte disturbances seen in Addison's disease, including raised kidney values with dilute urine, altered sodium and potassium levels, lethargy, and poor appetite. Additionally, untreated Addison's disease may in some cases contribute to dehydration and reduced kidney perfusion over time.
Diabetes Mellitus in Dogs
Diabetes mellitus is another endocrine disorder affecting metabolic regulation, and both conditions can present with lethargy, weight loss, and increased drinking and urination. The two occasionally occur together as part of immune-mediated disease affecting more than one endocrine gland, and although each is managed through a different hormonal pathway, both may need consideration in the same diagnostic workup when metabolic signs are non-specific.
The page on this condition is being checked again and is offline for now.
Pancreatitis in Dogs
Pancreatitis can present with similar gastrointestinal signs to an Addisonian crisis (vomiting, lethargy, abdominal discomfort, and inappetence), making differentiation challenging in acute presentations. Both conditions may also cause electrolyte disturbances and benefit from fluid support as part of stabilisation.
Acute Kidney Injury
A weak, vomiting dog with raised kidney values, dilute urine and a high potassium level can have either an Addisonian crisis or acute kidney injury, and the two cannot be told apart without blood tests that include cortisol measurement. In Addison's disease the kidney values typically improve quickly with fluid therapy, which can hide the underlying cause if it is not tested for.
Protein-Losing Enteropathy
Dogs with the atypical form of Addison's disease can present with chronic diarrhoea, weight loss and low blood albumin and cholesterol, a picture that closely resembles protein-losing enteropathy. For this reason, cortisol testing is often part of investigating chronic gut disease with protein loss.
Acute Haemorrhagic Diarrhoea Syndrome (AHDS)
Sudden vomiting and bloody diarrhoea with dehydration and weakness can occur in both AHDS and an Addisonian crisis. AHDS typically concentrates the red cells, whereas dogs with Addison's disease often have a normal or low red cell count despite dehydration, but blood tests including cortisol measurement are needed to separate them.
An Addisonian crisis is the point at which this condition becomes life-threatening. Collapse, profound weakness, repeated vomiting or diarrhoea (sometimes bloody), pale gums or a low body temperature in a dog with known or suspected Addison's disease can reflect a combination of shock, low blood sugar and a raised potassium level that slows and disrupts the heartbeat. This picture can move from a quiet, flat dog to collapse within hours, and without treatment it can be fatal. With intravenous fluids and hormone replacement given promptly, most dogs recover from a crisis. The potassium level and its effect on the heart cannot be measured at home. They are found only through blood tests and an ECG, and a dog in crisis may have a normal rather than a fast heart rate, so a heart rate that seems unremarkable is not reassurance. An episode of weakness or vomiting that settles on its own is not reassurance either, because the pattern in this condition is for episodes to recur, and a later one may not settle. In a dog already diagnosed, a crisis is more likely when a DOCP injection is overdue, when daily tablets have been missed, when vomiting or diarrhoea stops tablets being absorbed, and during illness, surgery, boarding or travel, which raise the body's need for cortisol. Over the longer term, an individual dog's triggers and early signs tend to become clearer, and many dogs with well-managed Addison's disease live full, active lives.
Last reviewed: 9 October 2026 · Dr Alastair Greenway MRCVS