📋 At-a-Glance Guide

What exactly happens inside a cat with Addison's disease?

Addison's disease occurs when the adrenal glands — two small hormone-producing structures perched just in front of the kidneys — stop manufacturing enough of two essential hormones: cortisol, which regulates metabolism and the stress response, and aldosterone, which controls the body's balance of sodium and potassium (VCA Animal Hospitals, 2023). The adrenal cortex, the outer layer of the gland, is subdivided into three zones, each producing a different class of steroid hormones. When immune-mediated destruction targets the adrenal tissue, all three zones can be affected, but the loss of mineralocorticoid and glucocorticoid production is what drives the clinical picture (Merck Veterinary Manual, 2024).

Without adequate aldosterone, potassium builds up in the bloodstream while sodium is lost through the kidneys. This electrolyte imbalance can slow the heart, weaken muscle contractions, and eventually trigger a life-threatening adrenal crisis. Cortisol deficiency, meanwhile, leaves the cat unable to mount a normal stress response, which is why even minor stressors — a vet visit, a new pet in the house, a change in routine — can tip a stable cat into collapse (Bruyette, 2018).

Diagnostic decision pathway for suspected feline hypoadrenocorticism

Which cats are most likely to develop Addison's disease?

Unlike dogs, where certain breeds such as Standard Poodles and Portuguese Water Dogs are overrepresented, feline hypoadrenocorticism shows no clear breed predisposition. The disease is most commonly diagnosed in middle-aged cats, though cases have been reported in animals as young as a few months and as old as 16 years (VCA Animal Hospitals, 2023). Males and females appear equally affected. Because the condition is rare, many veterinarians may go years without seeing a confirmed case, which contributes to diagnostic delays — affected cats often experience clinical signs for a median of 14 days before the disease is identified (dvm360, 2025).

What signs should make an owner suspect Addison's disease?

The hallmark of feline Addison's is its frustrating inconsistency. A cat may have several days of lethargy and poor appetite, seem to recover on her own, then relapse a week or two later. Weight loss is common and often progressive. Vomiting occurs in some cats, but diarrhea — a frequent sign in dogs with Addison's — is rarely seen in affected cats (VCA Animal Hospitals, 2023). On physical examination, a veterinarian may find dehydration, a slow heart rate (bradycardia), weak pulses, and noticeable loss of muscle mass and body fat. Up to 40% of cats present in a state of shock, with severe weakness, prolonged capillary refill time, and collapse — the classic adrenal crisis (dvm360, 2025).

How do veterinarians confirm an Addison's diagnosis?

Bloodwork often provides the first clue. The classic pattern is hyponatremia (low sodium) and hyperkalemia (high potassium), though not every Addisonian cat shows this combination. Kidney values may be elevated, and the urine is typically dilute — a pattern that can easily be mistaken for renal failure (Merck Veterinary Manual, 2024). The definitive test is the ACTH stimulation test: a baseline blood cortisol level is measured, synthetic ACTH is injected, and a second cortisol measurement is taken one to two hours later. A normal cat will show a robust rise in cortisol; a cat with Addison's will show little to no response, confirming that the adrenal glands cannot produce cortisol on demand (VCA Animal Hospitals, 2023).

What does treatment involve, both in a crisis and long-term?

An adrenal crisis is a medical emergency. Treatment begins with aggressive intravenous fluid therapy to correct dehydration and electrolyte imbalances. Steroids may be given, though veterinarians prefer to collect blood for the ACTH stimulation test before administering them whenever the cat is stable enough to wait (VCA Animal Hospitals, 2023). Once the crisis is controlled, lifelong hormone replacement begins. Cats typically need two medications: a glucocorticoid such as prednisolone to replace cortisol, and a mineralocorticoid — either daily oral fludrocortisone acetate (Florinef) or a long-acting injection of desoxycorticosterone pivalate, DOCP (Percorten-V), given approximately every 25 days (Merck Veterinary Manual, 2024).

What does long-term monitoring look like for an Addisonian cat?

Cats with hypoadrenocorticism require regular veterinary follow-up for the rest of their lives. In the early months after diagnosis, electrolyte levels are checked frequently — often monthly — to fine-tune the mineralocorticoid dose. Once the cat is stable, monitoring may decrease to every three to six months. Owners must also learn to recognize early signs of decompensation and understand that stress can trigger a crisis; veterinarians often recommend temporarily increasing the glucocorticoid dose during stressful events such as boarding, travel, or the introduction of a new household pet (Merck Veterinary Manual, 2024).

What symptoms mean this cat needs emergency care tonight?

Any cat with known Addison's disease who becomes acutely lethargic, refuses food for more than 24 hours, begins vomiting, or appears weak or wobbly should be seen by a veterinarian immediately. Collapse, pale gums, a heart rate that feels unusually slow, or any sign of disorientation constitutes a true emergency. Even in cats without a prior diagnosis, the combination of profound weakness, dehydration, and a slow heart rate warrants urgent evaluation — an undiagnosed Addisonian crisis can be fatal within hours if left untreated (dvm360, 2025).

Bottom line

Addison's disease in cats is rare but treatable. Once a cat survives the initial crisis and is started on appropriate hormone replacement, the prognosis is generally good, and most cats go on to live normal lifespans (VCA Animal Hospitals, 2023). The key is recognizing the subtle, intermittent signs before a crisis occurs — and when in doubt, running an ACTH stimulation test. Cases associated with adrenal tumors carry a poorer prognosis, but these are exceedingly uncommon. For the vast majority of Addisonian cats, a daily pill or monthly injection is all that stands between illness and a full, active life.

Addison's disease in cats is considerably rarer than in dogs, and the clinical presentation can be frustratingly nonspecific. Affected cats may show intermittent lethargy, decreased appetite, weight loss, and vague gastrointestinal signs that wax and wane over weeks to months. The disease results from inadequate production of glucocorticoids and mineralocorticoids by the adrenal cortex, most commonly due to immune-mediated destruction of the adrenal glands. Because cortisol plays a critical role in maintaining blood pressure, glucose homeostasis, and the body's response to stress, deficient production can lead to life-threatening electrolyte imbalances and cardiovascular collapse during periods of illness or stress. The classic electrolyte pattern of hyponatremia and hyperkalemia, while common in dogs with Addison's, is less consistently seen in cats, making the diagnosis even more challenging in feline patients (Merck Veterinary Manual, 2025; Cornell University College of Veterinary Medicine, 2021). Definitive diagnosis requires an ACTH stimulation test, which demonstrates an inadequate cortisol response to synthetic ACTH administration. Baseline cortisol levels alone are insufficient for diagnosis, as cats with other chronic illnesses may have low resting cortisol without true adrenal insufficiency. Treatment involves lifelong replacement of both glucocorticoids and mineralocorticoids. Prednisolone is typically used for glucocorticoid supplementation, with doses increased during periods of stress, illness, or surgery. Mineralocorticoid replacement is achieved with either desoxycorticosterone pivalate injections every 25 to 28 days or oral fludrocortisone. Owners must be educated about the importance of never skipping doses and seeking veterinary care promptly when their cat shows signs of illness, as Addisonian cats can decompensate rapidly without adequate steroid support (Merck Veterinary Manual, 2025).

The long-term management of feline Addison's disease requires a committed owner and a consistent veterinary partnership. Cats on DOCP injections need regular electrolyte monitoring to ensure the dosing interval is appropriate, as some cats require injections every 21 days rather than the standard 25 to 28 days. Cats on oral fludrocortisone require periodic electrolyte checks and blood pressure monitoring, as this medication has both mineralocorticoid and glucocorticoid activity. All Addisonian cats should have a stress plan in place, with clear instructions for increasing prednisolone doses during illness, travel, boarding, or any situation that increases physiological stress. Owners should keep injectable steroids at home if they live far from emergency care, and they should understand that vomiting, diarrhea, or lethargy in an Addisonian cat is never just a minor upset but a potential crisis. With diligent management, most cats with Addison's disease can live normal lifespans and enjoy good quality of life (Merck Veterinary Manual, 2025; Cornell University College of Veterinary Medicine, 2021).

The diagnostic journey for feline Addison's disease often begins with a cat who simply does not seem right. The veterinarian may find a cat who is quiet, perhaps slightly dehydrated, with no obvious explanation on physical examination. Initial bloodwork may reveal the classic findings of hyponatremia and hyperkalemia, though as noted, this pattern is less consistent in cats than in dogs. When these electrolyte changes are present, the sodium-to-potassium ratio can be a useful screening tool, with ratios below 27 raising suspicion for hypoadrenocorticism. However, definitive diagnosis always requires an ACTH stimulation test, and treatment should never be delayed in a cat who is clinically unstable while waiting for test results. In an Addisonian crisis, treatment begins with intravenous fluids to correct dehydration and electrolyte imbalances, glucocorticoid supplementation, and careful cardiac monitoring due to the risk of hyperkalemia-induced arrhythmias (Merck Veterinary Manual, 2025).

References

Bruyette, D. (2018, August). Disorders of the Adrenal Glands in Cats. Merck Veterinary Manual. https://www.merckvetmanual.com/cat-owners/hormonal-disorders-of-cats/disorders-of-the-adrenal-glands-in-cats

dvm360. (2025). Feline hypoadrenocorticism: Yes, cats get Addison's disease too. https://www.dvm360.com/view/feline-hypoadrenocorticism-yes-cats-get-addison-s-disease-too

Merck Veterinary Manual. (2024). Addison Disease (Hypoadrenocorticism) in Animals. https://www.merckvetmanual.com/endocrine-system/the-adrenal-glands/addison-disease-hypoadrenocorticism-in-animals

VCA Animal Hospitals. (2023, March 6). Addison's Disease in Cats. https://vcahospitals.com/know-your-pet/addisons-disease-in-cats