What are the signs of Addison's disease in cats?

Signs are often vague and insidious: lethargy and weakness, poor appetite and weight loss, vomiting and occasionally diarrhea, increased thirst and urination (from sodium loss), and muscle weakness or reluctance to move. Unlike dogs, cats may show more subtle behavioral changes — hiding, reduced grooming, and less social interaction — before more obvious clinical signs develop. An Addisonian crisis presents as acute collapse, profound weakness, bradycardia, and shock.

How is Addison's disease diagnosed in cats?

Diagnosis starts with bloodwork showing hyponatremia (low sodium), hyperkalemia (high potassium), and a Na:K ratio below 27. Elevated BUN and creatinine from prerenal azotemia, mild hypoglycemia, and a lack of a stress leukogram (lymphocytes and eosinophils are normal or elevated despite illness) are other clues. The diagnosis is confirmed with an ACTH stimulation test: synthetic ACTH is injected and cortisol measured before and 60 minutes after. In Addison's, cortisol fails to rise appropriately.

How is Addison's disease treated in cats?

An Addisonian crisis is treated with IV saline (0.9% NaCl) to correct electrolytes and restore blood pressure, and dexamethasone for immediate glucocorticoid replacement. Long-term management mirrors the dog protocol: DOCP (Percorten-V) injections every 25–28 days for mineralocorticoid replacement, plus daily prednisolone (not prednisone — cats cannot efficiently convert prednisone to its active form) for glucocorticoid replacement. Fludrocortisone is an oral alternative covering both. Stress dosing of prednisolone is required during illness or major stressors.

Why is prednisolone used instead of prednisone in cats with Addison's disease?

Prednisone is a prodrug that must be converted to its active form, prednisolone, by the liver. Dogs do this conversion efficiently. Cats have reduced hepatic ability to make this conversion, meaning prednisone is less reliably bioavailable in cats. Prednisolone is already in its active form and is absorbed predictably. For any cat requiring corticosteroids — including Addisonian cats on daily glucocorticoid replacement — prednisolone is the preferred choice over prednisone.

What is the prognosis for cats with Addison's disease?

Excellent — cats that receive appropriate treatment typically recover well and live normal-length lives. The condition requires lifelong medication (monthly DOCP injections and daily prednisolone, or daily fludrocortisone) and periodic electrolyte monitoring, but the management is straightforward once the correct doses are established. The main risks are a crisis from missed medication or failure to stress-dose during illness — both are preventable with owner education and adherence.

Addison's Disease in Cats: Symptoms, Diagnosis & Treatment (2026)

Q: What is Addison's disease in cats?

Addison's disease (hypoadrenocorticism) in cats is failure of the adrenal glands to produce sufficient cortisol (glucocorticoid) and, in most cases, aldosterone (mineralocorticoid). It is rare in cats — far less common than in dogs — but causes similar signs: vomiting, lethargy, weakness, poor appetite, and in severe cases, acute collapse (Addisonian crisis). Without treatment it is life-threatening, but with appropriate lifelong medication, cats do very well.

Quick Facts: Addison's Disease in Cats

What it is: Adrenal gland failure — too little cortisol and usually too little aldosterone. The opposite of Cushing's disease.
Rare in cats: Much less common than in dogs, but clinically significant and treatable when identified
Classic bloodwork flag: Low sodium + high potassium. Na:K ratio below 27 warrants ACTH stimulation testing.
Key diagnostic clue: No stress leukogram despite a clearly sick cat — lymphocytes and eosinophils normal or elevated
Diagnosis: ACTH stimulation test — cortisol fails to rise after synthetic ACTH injection
Treatment: DOCP injection every 25–28 days + daily prednisolone (not prednisone — cats convert it poorly)
Prognosis: Excellent — cats on consistent treatment live normal lives

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Addison's disease is rare enough in cats that many vets see only a handful of cases in an entire career. But when it does occur, it follows the same pathophysiology as in dogs — adrenal gland failure, electrolyte crisis, and acute collapse — and it responds to the same treatment approach. The key difference is how cats metabolize corticosteroids: prednisolone, not prednisone, is the right choice. Here is what feline Addison's looks like and how it is managed.

What Is Addison's Disease?

Addison's disease — medically hypoadrenocorticism — is failure of the adrenal cortex to produce its two essential hormone classes:

Glucocorticoids (primarily cortisol)

Control metabolism, blood glucose, immune modulation, and the physiological stress response. A cat without cortisol cannot manage even routine stressors — a vet visit, a car journey, or a bout of vomiting can destabilize the body in ways a healthy cat would handle easily.

Mineralocorticoids (primarily aldosterone)

Regulate sodium and potassium balance through the kidneys. Aldosterone instructs the kidney tubules to retain sodium and excrete potassium. Without it, sodium is lost in urine and potassium builds up in the blood — producing hyponatremia and hyperkalemia, and in severe cases, cardiac arrhythmias from the high potassium.

Typical vs. Atypical Addison's in Cats

As in dogs, most cats with Addison's have typical hypoadrenocorticism — deficiency of both cortisol and aldosterone, producing the characteristic electrolyte abnormalities. A subset have atypical hypoadrenocorticism — cortisol deficiency with normal electrolytes. Atypical cases are harder to recognize because the Na:K ratio is normal, and direct cortisol testing is needed. Some atypical cats later develop mineralocorticoid deficiency.

Causes in Cats

•Immune-mediated destruction (most common): The immune system destroys the adrenal cortex. This accounts for the majority of spontaneous feline Addison's, as in dogs.
•Iatrogenic — abrupt steroid withdrawal: Long-term corticosteroid use suppresses the HPA axis. Sudden discontinuation leaves the adrenal glands unable to produce cortisol. Note: cats are more resistant to exogenous steroid suppression than dogs, but prolonged or high-dose steroid use can still cause this.
•Over-treatment of Cushing's disease: Trilostane used to manage feline hyperadrenocorticism can over-suppress adrenal function. This requires monitoring with ACTH stimulation tests during treatment.
•Adrenal hemorrhage or infarct: Bilateral adrenal destruction from trauma, coagulopathy, or hemorrhagic necrosis — rare.
•Granulomatous disease or neoplasia: Bilateral adrenal infiltration by fungal disease or metastatic cancer — uncommon but reported.

How Feline Addison's Differs From Canine Addison's

Feature	Cats	Dogs
Prevalence	Rare	Uncommon but regularly diagnosed
Breed predisposition	None well established; DSH overrepresented by prevalence	Standard Poodle, Portuguese Water Dog, Bearded Collie
Presentation style	Often more insidious — subtle behavioral changes before GI signs	Classic waxing-waning GI signs; more recognizable pattern
Electrolyte pattern	Same — hyponatremia, hyperkalemia, Na:K <27	Same
Glucocorticoid of choice	Prednisolone — cats convert prednisone poorly	Prednisone or prednisolone — both work well in dogs
Steroid iatrogenic risk	Lower — cats are more resistant to exogenous steroid suppression	Higher — dogs suppress more readily with prolonged steroids
ACTH stim protocol	Same test; same interpretation criteria	Same

Symptoms of Addison's Disease in Cats

Cats are adept at concealing illness, and Addison's in cats can be particularly subtle in its early stages. Owners may notice behavioral changes before obvious clinical signs appear.

Chronic and Subacute Signs

•Lethargy and weakness: Variable energy, sometimes profoundly tired. Reluctance to jump or move normally.
•Poor appetite and weight loss: Gradual reduction in food intake and body condition over weeks to months.
•Vomiting: Episodic, sometimes attributed to hairballs or dietary issues. May recur periodically.
•Behavioral changes: Hiding, reduced grooming, less social interaction, withdrawal — often preceding obvious clinical signs in cats.
•Increased thirst and urination: Sodium wasting drives some PU/PD, though this is less dramatic than in diseases like hyperthyroidism or CKD.
•Muscle weakness and wasting: Cortisol deficiency leads to muscle protein breakdown and progressive weakness.
•Episodic improvement with supportive care: Like in dogs, the cat may temporarily improve with fluids or anti-nausea medication, then decline again — the waxing-waning pattern should prompt investigation.

Warning

The Addisonian Crisis in Cats

When cortisol and aldosterone levels fall critically low — often triggered by a stressor such as illness, boarding, travel, or surgery — a cat can deteriorate rapidly into an Addisonian crisis: profound weakness, inability to stand, bradycardia (slow heart rate from severe hyperkalemia), cold extremities, and cardiovascular collapse. This is immediately life-threatening. Any cat that collapses suddenly, especially with a history of chronic GI signs or lethargy, requires emergency veterinary care immediately.

Bloodwork Findings in Feline Addison's

Routine bloodwork provides the most important early clues. When a cat is sick but the electrolyte pattern and white cell count don't fit the usual picture, Addison's should be on the differential. For a full reference on what each value means, see our guide to reading cat blood test results.

Test	Finding	Why
Sodium (Na)	Low (hyponatremia)	Aldosterone deficiency → kidneys cannot retain sodium → lost in urine
Potassium (K)	High (hyperkalemia)	Aldosterone deficiency → kidneys cannot excrete potassium → accumulates
Na:K ratio	<27 (often <24)	Calculated from sodium ÷ potassium; normal is 27–40; below 27 warrants ACTH stim testing
BUN / Creatinine	Elevated	Prerenal azotemia from dehydration and reduced perfusion; typically resolves with IV fluids
Blood glucose	Low-normal or mildly low	Cortisol deficiency → impaired gluconeogenesis and glucose counterregulation
CBC — leukogram	Normal or lymphocytosis + eosinophilia	Sick cats should have a stress leukogram (high neutrophils, low lymphocytes). The absence of this — or a normal/reverse pattern — is a critical clue pointing to cortisol deficiency.
Calcium	Mildly elevated in some cases	Mechanism not fully understood; resolves with hormone replacement

Note

Ruling Out Urethral Obstruction

Severe hyperkalemia in cats is most commonly caused by urethral obstruction — a blocked bladder is far more common than Addison's in cats. Any hyperkalemic cat should be examined immediately for a distended, painful bladder. If no obstruction is found, Addison's and other causes of hyperkalemia (acute kidney injury, severe acidosis, massive tissue breakdown) move up the differential list and ACTH stimulation testing is appropriate.

How Vets Diagnose Addison's Disease in Cats

ACTH stimulation test — the definitive test

The same protocol used in dogs applies to cats. A baseline cortisol sample is drawn, synthetic ACTH (cosyntropin) is injected, and cortisol is remeasured 60 minutes later. In a healthy cat, cortisol rises substantially. In Addison's disease, both the baseline and post-ACTH cortisol are very low — the adrenal cortex cannot respond because it is destroyed or suppressed.

The test takes 60–90 minutes and can be run alongside emergency stabilization. Critically, dexamethasone can be given for glucocorticoid replacement before or during the test without interfering with the cortisol assay — so there is no reason to delay glucocorticoid treatment while waiting for results in a sick cat.

Resting cortisol as a screen

A single resting cortisol below 2 µg/dL in a cat with compatible clinical signs is highly suggestive of Addison's. A level above 2 µg/dL makes Addison's much less likely. This can be used as a rapid initial screen when the full ACTH stim is not immediately available, but a full ACTH stimulation test is needed for confirmation.

Other diagnostics

Urinalysis checks for urethral obstruction as a cause of hyperkalemia. Abdominal ultrasound assesses adrenal gland size — small adrenals suggest atrophy from chronic destruction (typical immune-mediated Addison's). ECG monitoring is important in any cat with severe hyperkalemia to detect cardiac arrhythmias. An electrocardiogram showing bradycardia, absent P waves, widened QRS complexes, or a sine-wave pattern indicates dangerous hyperkalaemia requiring immediate intervention.

Treatment of Addison's Disease in Cats

Emergency stabilization

Acute crisis treatment in cats mirrors the dog protocol:

•IV saline (0.9% NaCl): Corrects sodium, dilutes potassium, restores blood pressure and perfusion. Often produces rapid clinical improvement.
•Dexamethasone IV: Immediate glucocorticoid support without interfering with the ACTH stimulation test cortisol assay.
•Dextrose: Added to IV fluids if hypoglycemia is present.
•Cardiac monitoring: Continuous ECG for cats with severe hyperkalemia. Calcium gluconate protects the heart from arrhythmias while potassium is being corrected by fluids.

Long-term maintenance

DOCP (Percorten-V) — mineralocorticoid replacement

Injected subcutaneously or intramuscularly every 25–28 days. Replaces aldosterone — controls sodium retention and potassium excretion. Electrolytes are rechecked at each injection visit to confirm the Na:K ratio has normalized (>27) and to adjust the dose if needed. DOCP has no glucocorticoid activity, allowing the prednisolone dose to be managed independently.

Prednisolone — glucocorticoid replacement (not prednisone)

Given orally once daily at a low physiologic dose (typically 0.1–0.2 mg/kg/day). Prednisolone — not prednisone — is the correct choice for cats. Prednisone is a prodrug that requires hepatic conversion to its active form (prednisolone). Dogs make this conversion efficiently; cats do not. Prednisolone is already in its bioavailable active form and is absorbed predictably in cats. During illness, surgery, or significant stress, the dose must be doubled or tripled (stress dosing) to meet the increased cortisol demand the adrenal glands cannot provide.

Fludrocortisone (Florinef) — oral alternative

An oral tablet given once or twice daily that provides both mineralocorticoid and glucocorticoid activity. Simpler for some owners — daily tablets rather than monthly injections. Some cats need additional prednisolone supplementation. Both the DOCP + prednisolone approach and fludrocortisone are clinically valid; the choice depends on individual cat tolerance, owner preference, and cost considerations.

Stress dosing — essential owner knowledge

Cats with Addison's depend on their daily prednisolone to cover baseline cortisol needs. During any significant stressor — illness, surgery, hospitalization, travel, boarding — cortisol demand increases but the adrenal glands cannot respond. The prednisolone dose must be doubled or tripled for the duration of the stressor, then returned to maintenance once the cat is well.

If a cat is vomiting and cannot take oral medication, the situation becomes urgent — injectable glucocorticoid replacement must be given by a vet. Owners of Addisonian cats should have a crisis plan established with their vet, know the signs of deterioration, and be aware of which emergency clinics in their area have the knowledge and supplies to manage feline Addison's.

Warning

Never Stop Prednisolone Abruptly or Miss a DOCP Injection

An Addisonian cat without medication can deteriorate rapidly, especially under stress. Missed injections, accidental lapse in medication, or failure to stress-dose during illness can precipitate a life-threatening crisis. Inform all caregivers — boarding facilities, pet sitters, and emergency vets — of the diagnosis and medication requirements.

Long-Term Monitoring

Once stable on the correct doses, most cats need routine rechecks every 3–6 months:

•Electrolytes at each DOCP injection: Sodium and potassium checked before each monthly injection to confirm the Na:K ratio is normalizing and the dose is appropriate.
•Kidney values: Confirm the prerenal azotemia has resolved and remains stable.
•Clinical assessment: Body weight, muscle condition, thirst, energy, appetite — to ensure the prednisolone dose is neither too high (causing iatrogenic Cushing's signs) nor too low (inadequate cortisol replacement).
•Annual comprehensive bloodwork: Full chemistry panel and CBC once a year to assess overall health.

Prognosis

The prognosis for Addison's disease in cats is excellent. Cats that receive appropriate treatment and consistent long-term medication typically recover fully and live normal-length lives. The disease itself does not shorten lifespan when properly managed.

The main challenges are the lifelong commitment to monthly injections and daily medication, the importance of stress dosing, and ensuring all caregivers are educated about the condition. Owners who understand the disease and maintain the treatment routine consistently report their cats living full, active, and apparently normal lives after diagnosis.

Frequently Asked Questions

What is Addison's disease in cats?

Addison's disease (hypoadrenocorticism) is failure of the adrenal glands to produce sufficient cortisol and, in most cases, aldosterone. It is rare in cats but causes the same signs as in dogs: lethargy, vomiting, poor appetite, weight loss, electrolyte abnormalities (low sodium, high potassium), and in severe cases, acute collapse. It is life-threatening without treatment but responds very well to lifelong hormone replacement.

How do vets diagnose Addison's disease in cats?

The ACTH stimulation test is the gold standard. A baseline cortisol is measured, synthetic ACTH is injected, and cortisol is remeasured 60 minutes later. In Addison's, both values are very low — the adrenal glands cannot respond. Supporting findings on routine bloodwork include hyponatremia, hyperkalemia (Na:K ratio below 27), elevated BUN/creatinine, mild hypoglycemia, and a normal or reversed white cell pattern (no stress leukogram) despite obvious illness.

Why prednisolone and not prednisone for cats with Addison's?

Prednisone is a prodrug that must be converted by the liver into its active form, prednisolone. Dogs perform this conversion efficiently. Cats have reduced hepatic ability to make this conversion, meaning prednisone is less bioavailable and less predictably effective in cats. Prednisolone is already in its active form and is absorbed reliably. All corticosteroid therapy in cats — including glucocorticoid replacement for Addison's — should use prednisolone rather than prednisone.

What is the difference between Addison's and Cushing's disease in cats?

They are opposite conditions. Cushing's disease (hyperadrenocorticism) involves excess cortisol production, causing fragile skin, a pot belly, hair loss, and insulin-resistant diabetes. Addison's disease (hypoadrenocorticism) involves insufficient cortisol and aldosterone production, causing weakness, vomiting, electrolyte abnormalities, and collapse. Cushing's is treated by blocking cortisol; Addison's is treated by replacing it.

What happens if a cat with Addison's disease misses medication?

Missing a DOCP injection or stopping prednisolone abruptly — especially during illness or stress — can rapidly precipitate an Addisonian crisis: profound collapse, bradycardia, shock, and cardiovascular failure. This is a medical emergency. Addisonian cats must receive their medication consistently, all caregivers must be informed of the diagnosis, and a crisis plan (including which emergency vet to contact) should be established with the primary vet.

Can cats with Addison's disease live normal lives?

Yes — the prognosis is excellent. Cats on consistent DOCP injections and daily prednisolone typically recover fully and live normal-length lives with no significant impact on daily quality of life. The condition requires lifelong management and periodic monitoring, but cats adapt well and owners routinely report their cats are back to completely normal behavior after stabilization.

Want to understand your cat's electrolyte and bloodwork results?

Upload your cat's chemistry panel or CBC — VetLens explains every value in plain language, flags abnormal sodium and potassium, and helps you track changes at each vet visit.