Why?
In dogs, grapes can cause acute kidney failure, and there's no way to predict which animal will react or how much it takes. The mechanism isn't fully understood, though tartaric acid is currently a leading suspect. Data in cats is scarce, but cases have been reported, so the same rule applies to be safe.
How much?
No amount is considered safe, whether green, red, organic, seeded or seedless. Keep bunches out of reach, fruit bowl included.
The risks
- Acute kidney damage (described in dogs)
- Vomiting and diarrhea
- Lethargy and loss of appetite
- Abnormal thirst or urination, or no urine at all
Your cat ate some: what now?
Call your vet or an animal poison control center right away, even for a single grape and even if your cat seems fine. Note what was eaten, how much and when. Don't try to make your cat vomit yourself: let the vet decide.
Better options
If your cat loves batting at and nibbling small round things, a couple of blueberries are a safe swap. A cat treat or a bit of plain cooked chicken works just as well.
Common questions
My cat ate one grape, what should I do?
There's no known safe dose, and sensitivity varies between animals. One grape won't necessarily cause harm, but call your vet for advice rather than waiting.
Are seedless or peeled grapes safe?
No. In dogs, problems have been reported with all kinds of grapes, seedless and peeled included, so none are considered safe for cats either.
This information is general and does not replace advice from a veterinarian. If your cat has swallowed something toxic, call your vet or an animal poison control center right away, without waiting for symptoms.