# Spironolactone for Cats With Hyperaldosteronism Spironolactone for cats with hyperaldosteronism is an aldosterone antagonist, a medicine that blocks the hormone aldosterone at its receptor. It is used to control the high blood pressure and dangerously low potassium caused by an aldosterone-secreting adrenal tumor, and it is often given before surgery to remove that tumor. It is one part of treatment, not a cure on its own. This article is educational and is not a substitute for veterinary diagnosis or treatment. ## Quick Answer - Spironolactone is a potassium-sparing diuretic that blocks aldosterone, the hormone that is overproduced in feline primary hyperaldosteronism (also called Conn's syndrome in people) [1]. - It helps protect against hypokalemia (low blood potassium) and systemic hypertension, the two most common problems caused by this rare adrenal condition [1]. - It is frequently used as preoperative stabilization. In one multi-institution study, 55% of cats having adrenal surgery received spironolactone beforehand [2]. - Your veterinarian sets the dose from your cat's weight, potassium level, kidney values, and blood pressure. Never adjust it on your own. - Cats on spironolactone need periodic blood tests to check potassium, kidney values, and blood pressure, plus monitoring for skin or coat changes. ## What Is Spironolactone and Why Do Veterinarians Use It in Cats? Spironolactone is a diuretic, which means it helps the body move sodium and water out through the urine. What makes it different from common diuretics like furosemide is that it also blocks aldosterone, so it holds potassium in the body instead of flushing it out. In a cat with primary hyperaldosteronism, an adrenal tumor (or, less often, overgrowth of the adrenal tissue) releases aldosterone without any normal off switch [1]. Aldosterone tells the kidneys to keep sodium and dump potassium. The result is high blood pressure and low blood potassium, which can cause weakness, lethargy, and the head-down posture called neck ventroflexion [1][2]. Spironolactone interrupts that signal at the receptor level. It does not shrink the tumor and it does not stop aldosterone from being made. Instead, it blunts the hormone's effects so the body can hold on to potassium and the blood pressure is easier to control [1]. Veterinarians use it in a few situations: - Before adrenal surgery, to correct hypokalemia and hypertension so the cat is stable enough for anesthesia [2] - When surgery is not possible, as part of long-term medical management alongside potassium supplements and blood pressure medication [1] - When a cat has an adrenal mass that cannot be removed safely, or when the cat's overall health makes surgery too risky Surgery to remove the affected adrenal gland is the treatment that addresses the root cause, and many cats improve after it [2]. Spironolactone buys time and reduces risk in the meantime. ## How Spironolactone Works in Cats Aldosterone normally binds to receptors in the kidney's tubules. When it docks there, the kidney reabsorbs sodium and water and excretes potassium into the urine. Spironolactone is a competitive antagonist. It occupies those same receptors so aldosterone cannot bind. Sodium and water leave the body in the urine, and potassium stays in the blood where it belongs. This is why spironolactone is called a potassium-sparing diuretic. It is a weaker diuretic than furosemide, but its potassium-sparing action is exactly what a cat with hyperaldosteronism needs. Two points matter for owners: First, spironolactone does not lower aldosterone levels. If your veterinarian measures aldosterone in your cat's blood while it is taking spironolactone, the number can still be high. That is expected and does not mean the drug is failing. Second, blood pressure control often requires more than one medication. Many cats with primary hyperaldosteronism also need amlodipine, a calcium channel blocker, to bring systolic blood pressure down [2]. Spironolactone helps, but it is rarely enough by itself. Some cats with aldosterone-secreting tumors also have elevated progesterone and corticosterone, other adrenal hormones that can complicate the picture [3]. Your veterinarian may test for these if your cat's signs do not fully match expectations. ## Dosing Basics for Spironolactone in Cats ### Who decides the dose? Your veterinarian does. The dose depends on your cat's weight, potassium level, kidney function, blood pressure, and what other medications it takes. There is no single standard dose that fits every cat, and dosing in cats is not as well studied as it is in people or dogs. ### How is it given? Spironolactone is given by mouth, usually as a tablet or compounded liquid. It is typically given once or twice daily with food, because food improves absorption and reduces stomach upset. If your cat is hard to pill, talk to your veterinarian about compounding into a flavored liquid or a transdermal gel. Some cats with hyperaldosteronism also have hyperthyroidism, which means two daily medications. If pill time has become a battle, these tips on [giving your cat medication without the fight](/knowledge/veterinary-medicine/senior-and-chronic-care/cat-hyperthyroidism-medication-tips) can help. ### What if you miss a dose? Give the missed dose when you remember, unless it is almost time for the next one. In that case, skip the missed dose and go back to your regular schedule. Do not double up to catch up. Doubling can push potassium too high, which is dangerous. If you are unsure, call your veterinarian's office. They would rather answer a quick question than treat a complication. ### How long will my cat take it? That depends on the plan. If surgery is scheduled, spironolactone may be used for days to weeks before the operation [2]. If surgery is not an option, it may be lifelong. After adrenalectomy, some cats develop the opposite problem, low aldosterone, and need mineralocorticoid replacement instead. In one report, a cat needed mineralocorticoid therapy for 6 months after surgery for an adrenal carcinoma [4]. ## Side Effects of Spironolactone in Cats Most cats tolerate spironolactone reasonably well, but side effects do happen. The table below covers what owners most often see. | Side effect | How common or serious | What to do | |---|---|---| | Increased thirst and urination | Common, mild | Expected with a diuretic. Keep fresh water available. Mention it at your next visit if it is severe. | | Stomach upset, vomiting, reduced appetite | Common, usually mild | Give with food. Call your veterinarian if vomiting lasts more than a day or your cat stops eating. | | Lethargy or weakness | Can be a sign of potassium or blood pressure problems | Call your veterinarian the same day. This can also be a sign of the underlying disease worsening. | | High potassium (hyperkalemia) | Uncommon but serious | Only detected on blood work. This is why monitoring matters. | | Worsening kidney values | Possible, especially in cats with existing kidney disease | Detected on blood work. Your veterinarian will adjust the plan if values change. | | Skin changes, coat dullness, or a curling of the ear tips | Reported in cats on long-term spironolactone | Tell your veterinarian at a routine visit. Dose adjustment may help. | | Facial or generalized itching | Uncommon | Call your veterinarian. An antihistamine or a change of medication may be needed. | Serious reactions are uncommon, but they are the reason follow-up testing is not optional. Potassium that climbs too high can cause heart rhythm problems, and kidney values that worsen mean the dose or the whole plan needs a second look. ## Who Should Not Take Spironolactone, and What Interacts With It Spironolactone is not right for every cat. Your veterinarian will weigh the risks if your cat has: - **Kidney disease.** Cats with primary hyperaldosteronism often already have some kidney compromise, and spironolactone can raise potassium and creatinine further. One cat in a case report had pre-existing renal failure and developed low aldosterone after surgery, requiring mineralocorticoid therapy [4]. - **High potassium already.** If potassium is normal or high before starting, spironolactone can push it into a dangerous range. - **Dehydration or ongoing fluid losses.** Diuretics can worsen dehydration. - **Pregnancy or breeding.** Spironolactone is not recommended in breeding cats. Drug interactions matter too. Tell your veterinarian about everything your cat takes, including supplements. - **ACE inhibitors and angiotensin receptor blockers** (such as benazepril, enalapril, or telmisartan) also affect potassium and kidney function. Combining them with spironolactone raises the risk of hyperkalemia. Telmisartan is sometimes used in diagnostic testing for this condition, and it suppresses aldosterone differently in healthy cats than in cats with primary hyperaldosteronism [5]. - **Potassium supplements**, which many cats with hyperaldosteronism need, can stack with spironolactone and push potassium too high [2]. - **Other potassium-sparing diuretics** should not be combined. - **NSAIDs** can reduce kidney blood flow and worsen kidney values when combined with diuretics. If your cat also has heart disease, the medication plan gets more complex. Diuretics like furosemide can activate the renin-angiotensin-aldosterone system, and cats with cardiomyopathy already show higher aldosterone and renin activity than healthy cats [6]. If your cat has both conditions, your veterinarian will balance the heart medications against the adrenal problem. For background on the heart side, see [hypertrophic cardiomyopathy in cats](/knowledge/veterinary-medicine/clinical-methods/hypertrophic-cardiomyopathy-in-cats) and [heart disease diets for cats](/knowledge/veterinary-medicine/nutrition/heart-disease-diet-cats-low-sodium-and-taurine-supplementation). Steroids are a separate category. If your cat takes prednisolone for another condition, do not stop it without talking to your veterinarian first. For general information on that drug, see [prednisolone for cats](/knowledge/veterinary-medicine/calculators-clinical-tools/prednisolone-for-cats-feline-safe-steroid-dose-and-autoimmune). ## Overdose and When to Call for Help An overdose of spironolactone can cause vomiting, severe weakness, dehydration, and dangerously high potassium. Signs of high potassium include weakness, collapse, a slow heart rate, or an irregular heartbeat. If you think your cat ate extra tablets, call your veterinarian or an animal poison control hotline right away. Do not wait for symptoms. - **ASPCA Animal Poison Control Center:** (888) 426-4435 - **Pet Poison Helpline:** (855) 764-7661 Have the medication bottle with you so you can tell them the strength of the tablets and how many your cat may have eaten. Do not try to make your cat vomit unless a veterinarian tells you to. ## Limitations and When to Contact a Veterinarian Spironolactone treats the consequences of hyperaldosteronism, not the tumor itself. It can lower blood pressure and protect potassium, but it will not stop a malignant adrenal tumor from growing or spreading. About half of aldosterone-secreting tumors in cats are malignant, and spread to the lungs has been documented [7]. That is why imaging and follow-up matter as much as the medication. Call your veterinarian the same day if you see: - New or worsening weakness, wobbliness, or neck ventroflexion - Vomiting that lasts more than 24 hours or repeated vomiting - Your cat stops eating or drinking - Increased drinking and urination beyond what you saw before starting the medication - Any new medication or supplement added by another provider Go to an emergency clinic now if you see: - Collapse or inability to stand - Trouble breathing, open-mouth breathing, or a blue tint to the gums - A very slow or irregular heartbeat - A seizure - Sudden blindness, which can happen with severe high blood pressure Keep routine recheck visits even when your cat seems fine. Blood pressure, potassium, and kidney values can change without obvious signs at home. Your veterinarian will decide how often to test based on your cat's stability. Every cat is different, and only your veterinarian can decide whether spironolactone is right for your cat, at what dose, and for how long. ## Frequently Asked Questions ### Does spironolactone cure hyperaldosteronism in cats? No. Spironolactone blocks aldosterone's effects but does not remove the source of the excess hormone. Surgery to remove the affected adrenal gland is the treatment that addresses the cause, and spironolactone is often used to stabilize cats before that surgery [1][2]. If surgery is not possible, spironolactone becomes part of long-term management. ### How will I know if spironolactone is working? You may notice your cat is stronger, more active, and more like itself, especially if low potassium was causing weakness. Your veterinarian will confirm with blood pressure readings and blood tests for potassium and kidney values. Improvement in these numbers is the clearest sign the plan is working. ### Can spironolactone be used alone for this condition? Rarely. Most cats also need potassium supplementation and a blood pressure medication such as amlodipine [2]. The combination depends on how high the blood pressure is, how low the potassium is, and whether surgery is planned. Your veterinarian will build the plan around your cat's specific test results. ### What happens after adrenal surgery? Many cats improve, and some heart changes caused by the high blood pressure can reverse over months [8]. Some cats develop low aldosterone after surgery and need mineralocorticoid replacement for a period of time, which can last months [4]. Your veterinarian will check potassium and aldosterone after surgery to see which way your cat goes. ### Can I stop spironolactone if my cat seems better? Do not stop it on your own. Feeling better usually means the medication is doing its job, not that it is no longer needed. Stopping suddenly can let blood pressure and potassium swing back to dangerous levels. Talk to your veterinarian before any change, even if your cat looks completely normal. ## Related Articles - [Heart Disease Diet Cats: Low Sodium and Taurine Supplementation](/knowledge/veterinary-medicine/nutrition/heart-disease-diet-cats-low-sodium-and-taurine-supplementation) - [Prednisolone for Cats: Feline Safe Steroid Dose and Autoimmune](/knowledge/veterinary-medicine/calculators-clinical-tools/prednisolone-for-cats-feline-safe-steroid-dose-and-autoimmune) - [Cat Hyperthyroidism: How to Give Your Cat Medication Without the Fight](/knowledge/veterinary-medicine/senior-and-chronic-care/cat-hyperthyroidism-medication-tips) - [Hypertrophic Cardiomyopathy in Cats](/knowledge/veterinary-medicine/clinical-methods/hypertrophic-cardiomyopathy-in-cats) - [Canine Hyperadrenocorticism: Treatment Options and Monitoring](/knowledge/veterinary-medicine/clinical-internal-medicine/canine-hyperadrenocorticism-treatment-options-monitoring) - [Drug Interactions with Antidiabetic Medications in Dogs and Cats](/knowledge/veterinary-medicine/clinical-pharmacology/drug-interactions-antidiabetic-medications-dogs-cats) ## References 1. [Feline Primary Hyperaldosteronism - Endocrine System](https://www.merckvetmanual.com/endocrine-system/the-adrenal-glands/feline-primary-hyperaldosteronism). Merck Veterinary Manual. 2. [Surgical findings and outcomes after unilateral adrenalectomy for primary hyperaldosteronism in cats: a multi-institutional retrospective study](https://pubmed.ncbi.nlm.nih.gov/36706013/). Journal of feline medicine and surgery, 2023. 3. [Multiple corticosteroid abnormalities in cats with hyperaldosteronism](https://pubmed.ncbi.nlm.nih.gov/34331479/). Journal of veterinary internal medicine, 2021. 4. [Long-lasting hypoaldosteronism after adrenalectomy in a cat with hyperaldosteronism](https://pubmed.ncbi.nlm.nih.gov/38746623/). JFMS open reports, 2024. 5. [Prospective evaluation of a telmisartan suppression test as a diagnostic tool for primary hyperaldosteronism in cats](https://pubmed.ncbi.nlm.nih.gov/37246725/). Journal of veterinary internal medicine, 2023. 6. [Circulating renin-angiotensin-aldosterone system activity in cats with systemic hypertension or cardiomyopathy](https://pubmed.ncbi.nlm.nih.gov/35285549/). Journal of veterinary internal medicine, 2022. 7. [Immunohistochemistry confirms pulmonary metastases from an adrenal adenocarcinoma causing primary hyperaldosteronism in a cat](https://pubmed.ncbi.nlm.nih.gov/42499989/). JFMS open reports, 2026. 8. [Reversible right-sided congestive heart failure secondary to primary hyperaldosteronism in a cat](https://pubmed.ncbi.nlm.nih.gov/39128413/). Journal of veterinary cardiology : the official journal of the European Society of Veterinary Cardiology, 2024. ## Further Reading - [Disorders of the Adrenal Glands in Cats - Cat Owners (Merck Veterinary Manual)](https://www.merckvetmanual.com/cat-owners/hormonal-disorders-of-cats/disorders-of-the-adrenal-glands-in-cats) - [American Veterinary Medical Association: First Aid Tips for Pet Owners](https://www.avma.org/resources-tools/pet-owners/emergencycare/first-aid-tips-pet-owners) - [Merck Veterinary Manual: Cat Owners](https://www.merckvetmanual.com/cat-owners)