KidneyCats Supplements: a vet's honest take
The short answer
A short list has real evidence: omega-3 fatty acids, phosphorus binders sold as supplements, potassium and B vitamins where she's low, and probiotics as a maybe. Most of the rest are harmless and unproven, a few are a waste of money, and one or two can genuinely hurt her. Tell your vet about anything you're giving.
Do kidney supplements actually work for cats?
Some do. Most are unproven. A few can hurt her.
This is the area where the most money gets wasted in feline kidney disease, so I'd rather go through it honestly than either dismiss the whole category or nod along. And I want to be clear about the difference between two things people conflate: no evidence usually means nobody has done the study, not that the product has been tested and failed. Both are reasons to spend cautiously.
The ones worth the money
Fish oil. The strongest case in the category. Worth knowing that therapeutic kidney diets already have omega-3 added for exactly this reason, so if she's eating a renal diet, ask before adding more. If she isn't, ask your vet for a dose rather than guessing from a human bottle.
Practical notes: use a product made for pets, keep it in the fridge because it goes rancid and a rancid oil is worse than none, and avoid cod liver oil, which carries a lot of vitamin A and isn't the same thing as a fish body oil.
A phosphorus binder sold over the counter. Some of these are legitimate. The catch is that the dose has to be set against her actual phosphorus level and her stage, and it changes how her bloodwork should be interpreted. So this is a conversation with your vet, not a purchase. The full detail is on the phosphorus binders page.
B vitamins, usually as part of an appetite or general support product. Cheap, harmless, and there's a real rationale because she's losing water-soluble vitamins in a large volume of urine.
Potassium, but only on a blood value. This one gets its own page because it goes wrong in both directions: potassium. Never add it blind.
The ones that are probably fine and probably not doing much
I don't fight owners over these. If it's affordable and it makes you feel like you're doing something, that has some value of its own. Just don't let it displace real treatment.
Probiotics. The theory, sometimes called enteric dialysis, is that gut bacteria consume some nitrogen waste before it's absorbed. Mechanistically plausible, evidence in cats thin but not absent, cheap, harmless.
Antioxidant blends and general "renal support" formulas. Usually harmless. Read the label for potassium, calcium, vitamin D and vitamin A, because those four are the ones that matter, and check with your vet if any appear.
Astragalus, rehmannia and other traditional herbal formulas. Used widely in integrative practice, and there's some laboratory work. I'd want to know exactly what's in it, because herbal blends are variably manufactured and some contain more than the label says.
The ones I'd skip
Cranberry. Aimed at bladder infections, not kidneys, and the evidence for that is weak in cats anyway. It also acidifies urine, which is the wrong direction for a kidney cat already dealing with acid build-up. Skip it.
Milk thistle, unless her liver is the problem. It's a liver supplement. Kidney and liver are different organs.
Most appetite "stimulant" supplements. If she isn't eating, she's usually nauseated, and that needs a real antiemetic rather than a herbal appetite product. See nausea and vomiting.
Anything promising to repair, regenerate or restore kidney function. Nephrons don't grow back. There is no supplement, in any bottle, that reverses kidney damage, and a claim like that on a label tells you what the whole product is.
Colloidal silver, and anything sold on a testimonial rather than a mechanism. No.
The ones that can actually hurt her
This is the part that matters, so it's the part that gets a warning box.
How to evaluate one yourself
Three questions, and they'll sort most products in about ten seconds.
Does the label name a mechanism, or only a feeling? "Binds phosphorus in the gut" is a claim you can check. "Supports renal wellness" is not a claim at all.
Does it list amounts, per ingredient, per dose? A proprietary blend that won't say how much of anything is in it can't be dosed or assessed, and that's usually deliberate.
Would it change her bloodwork? If yes, it's medicine and your vet needs to know. If no, ask what you're paying for.
And the fourth, which isn't about the product: is anything real being displaced to afford it? That's the only version of a harmless supplement that actually does harm.
For where the money genuinely goes in this disease, and where the savings are, see what this actually costs.
Questions people ask me about this
- Do kidney supplements actually work for cats?
- A few do. Omega-3 fatty acids from fish oil have reasonable evidence for kidney blood flow and inflammation. Phosphorus binders sold as supplements genuinely bind phosphorus. Potassium and B vitamins help cats who are low in them. Beyond that the evidence thins out fast, and most of what's marketed for feline kidneys is unproven rather than proven useless.
- Is fish oil good for cats with kidney disease?
- Yes, it's the supplement with the best case behind it, and therapeutic kidney diets already have it added for that reason. If she's on a renal diet she may not need more. If she isn't, ask your vet about a dose. Use a product made for pets, keep it refrigerated because it goes rancid, and don't use cod liver oil, which is high in vitamin A.
- Should I give my cat a kidney support supplement I saw online?
- Tell your vet what's in it before you start. Some contain genuine phosphorus binders, which is fine but changes how her bloodwork should be read and needs dosing against her actual number. Others are a mix of herbs with no evidence. A few contain potassium, which is dangerous to add blind in a late-stage cat.
- Are there supplements that can harm a cat with kidney disease?
- Yes. Vitamin C in any real dose, because cats convert it to oxalate and that's a stone risk. Vitamin D or calcium without bloodwork, because the calcium and phosphorus balance is already disturbed. Extra potassium added blind, which is dangerous in late-stage disease. High-dose vitamin A. And several herbal products, including anything containing willow bark, which is aspirin-like.
- Does cranberry help a cat with kidney disease?
- No. Cranberry is aimed at bladder infections, not kidneys, and even for bladder infections the evidence in cats is weak. It also acidifies the urine, which is the wrong direction for a kidney cat who's already fighting acid build-up. This is one to skip.
- What about probiotics for kidney disease?
- Reasonable as a maybe. The idea, called enteric dialysis, is that gut bacteria consume some nitrogen waste so less is absorbed. The theory is sound and the evidence in cats is thin but not absent. It's cheap and harmless, so I don't argue with owners who want to try one. I wouldn't skip a real treatment to afford it.
Medically reviewed by Dr. Steve Pelton, last updated . First published . Reviewed quarterly.