The Canine Ledger

Grapes and Raisins: What We Know, and the Tartaric Acid Question

Most dogs who eat grapes are fine. Some die of kidney failure, and no one can say which in advance. What the studies show, and why you still phone at once.

Written by thecanineledger

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If your dog has just eaten grapes, raisins, sultanas or currants, in any amount: phone your vet, an emergency clinic or an animal poison helpline now. Have the packet or recipe to hand, and your dog’s weight. Don’t make your dog vomit unless a vet tells you to.

In the records of 64 UK emergency clinics, vets saw 31,425 dogs that had probably eaten grapes or their dried forms between 2018 and 2024. Of those, 0.9% died or were put to sleep (Altman et al., Frontiers in Veterinary Science 2026).

That is reassuring. It is also not the whole picture.

While most dogs who eat grapes come to no harm, the ones who do can go into kidney failure, and once a dog stops making urine, the Merck Veterinary Manual says “most dogs die or are euthanized”. Nobody can tell you in advance which kind of dog yours will be. This page covers what the studies show, the leading explanation for why grapes are toxic, and why the advice is still to phone straight away.

1. How often grapes actually harm dogs

Three studies give a sense of the odds. All three are of dogs who were taken to a vet, and most of those dogs were treated.

StudyDogsWhat happened
Dutch poisons centre, 2018 (Dijkman et al., Journal of Small Animal Practice 2022)9514.7% developed signs, mostly vomiting. One dog (1%) developed kidney injury.
Three US teaching hospitals, 2005–2014 (Reich et al., Journal of Veterinary Emergency and Critical Care 2020, abstract)139Of dogs with blood tests, “the prevalence of AKI was 6.7% (8/120)”. AKI is acute kidney injury.
64 UK emergency clinics, 2018–2024 (Altman 2026)31,425Mortality 0.9%.

The Reich authors conclude: “The prevalence of AKI and mortality was low in dogs with confirmed grape or raisin ingestion.”

Why this doesn’t mean “it’s fine”. In these studies most dogs had their stomachs emptied by a vet. In the Dutch study, 88% of dogs without signs were decontaminated, meaning made to vomit or given activated charcoal; in the US study, 88% overall. We don’t know how many would have been harmed without that treatment. The low figures are partly a measure of what vets did.

And for the dogs who are harmed, it is serious. In a Swiss study of 15 dogs already in severe kidney failure from grapes or raisins, 8 survived (Schweighauser et al., Journal of Veterinary Internal Medicine 2020).

Our note: These figures are low, but no safe amount is known. Phone anyway.

2. Why no one can predict it

For years, the reason grapes harm some dogs and not others was unknown. The Merck Veterinary Manual’s chapter now gives the leading explanation: “One proposed toxic principle in these fruits is tartaric acid” (Merck, Grape, Raisin, and Tamarind Toxicosis in Dogs).

Merck explains why dogs are particularly vulnerable: “Dogs poorly excrete organic acids because they lack the organic acid transporters that other species have, allowing tartaric acid to accumulate in the proximal renal tubular cells”, part of the kidney.

And it explains the unpredictability: “The tartaric acid content of grapes, raisins, and tamarinds varies, resulting in variable effects following ingestion.”

This is why we don’t print a safe amount. If the toxic part varies from fruit to fruit, a handful of grapes that did no harm last year is no guide to this year. Merck gives figures for vets. We have left them out.

→ Foods That Are Toxic to Dogs, With the Actual Evidence

3. The tartaric acid question

The tartaric acid idea came from an unexpected place. In 2022, a team using records from the ASPCA Animal Poison Control Center reported six dogs that developed kidney injury after eating tamarinds or cream of tartar, a baking ingredient. They describe tartaric acid as “the common denominator” (Wegenast et al., Journal of Veterinary Emergency and Critical Care 2022, abstract).

The kidney damage looked the same as in grape poisoning. The authors wrote that “Clinical signs, laboratory findings, and histopathologic lesions were similar to those reported in grape and raisin toxicosis.” Of the six dogs, “Four dogs were euthanized, and the outcome is unknown for 2 of the dogs.” They concluded that “tartaric acid is identified as the likely toxic component in grapes and tamarinds.”

How settled is it? Not fully. The evidence is a case series of six dogs, linked to what is known about grapes and about how dogs handle organic acids. Merck calls it “proposed”. It is the best explanation available, not a proven one.

What it means in practice. Merck now lists tamarind alongside grapes: “Tamarind (Tamarindus spp) ingestions have also resulted in renal failure in dogs.” If your dog eats tamarind, or a quantity of cream of tartar, treat it the same way as grapes, and phone.

Our note: A second case series (Bates et al., 2023) has the same title, but we couldn’t read its abstract. We haven’t found a source on play dough.

4. Fresh grapes, dried fruit, and currants

Fresh grapes may be the riskier form. Many owners assume raisins are worse, because they are concentrated. In the UK emergency study, fresh fruit was associated with higher mortality: the authors report that “Fresh fruit ingestion carries higher mortality risk in both species.” Raisins, currants and sultanas were eaten more often, and cases clustered in December.

That finding comes with caveats the authors set out. Records did not say how much was eaten or when, and “Mortality outcomes in this study did not distinguish euthanasia from unassisted death, nor capture illness severity, limiting interpretation.” So treat it as a reason not to relax about fresh grapes, not as proof that raisins are safe.

Which currants count. Dried “currants” in baking are Zante currants, a kind of grape, and they count. Merck notes that “Ingestion of true currants of the genus Ribes has not been associated with renal injury”. Those are fresh blackcurrants and redcurrants, a different plant. If you aren’t sure which your dog ate, assume the worse.

Our note: The fresh-versus-dried finding runs against what most owners believe. It is a reason not to relax about fresh grapes, not proof that raisins are safe.

5. The signs, and how fast

Merck: “Most dogs with grape, raisin, or tamarind toxicosis develop vomiting or diarrhea within 6–12 hours after ingestion.” Other signs include lethargy, not eating, drinking more, and dehydration.

Kidney failure follows. Merck says dogs can progress to producing little or no urine “within 24–72 hours after exposure”. It also warns that anuric dogs, those making no urine, “are unlikely to survive unless peritoneal dialysis or hemodialysis is initiated; even then, the prognosis is guarded.”

Some dogs show odd neurological signs. In the Swiss study of dogs with severe kidney failure from grapes, “Eleven dogs (73%) had marked forebrain, cerebellar, or vestibular signs”: problems such as wobbliness, head tilt, or seeming dull or disoriented. The authors suggest these signs are specific to grape poisoning and can recover.

→ Emergency Signs in Dogs: When to Go Now, Not Tomorrow

6. What to do

Phone first, before signs appear. Merck: “Prompt GI decontamination is the recommended treatment for raisin, grape, or tamarind toxicosis in patients that remain clinically normal.” That means making the dog vomit, under a vet’s control, while they are still well.

There is a window, and it is longer than you might think. In the Dutch study, vet-induced vomiting brought up grapes in 98% of dogs when given within four hours, and in 83% when given at four to twelve hours. The authors suggest “induction of emesis, may be warranted up to 12 hours after ingestion.” So if you only found the empty packet this morning, phone anyway.

In the UK study, decontamination stood out. The authors found it was “the strongest predictor of survival” in dogs. That is an association in records, not a trial, but it points the same way as everything else.

Don’t make your dog vomit at home. Merck lists drugs and doses for vets to use. We don’t print them. The vet will decide whether vomiting is safe for your dog, and do it properly.

→ My Dog Ate Something: Why You Shouldn’t Make Them Vomit Without a Vet · → Animal Poison Helplines by Country: Numbers, Fees, and What Works From Where

Expect blood tests. Merck’s treatment includes fluids into a vein and “Close monitoring of renal function”. Your vet may want to check kidney values over the next few days.

Our note: No safe amount is known, so phone for any amount, including one grape.

7. What we could not verify

Commonly saidWhat we found
“One grape can kill a dog”We found no source that sets either a fatal or a safe amount for owners. That is why we say phone for any amount.
“Raisins are more dangerous than grapes”Not in the largest study. Fresh fruit was linked to higher mortality, with caveats.
“My dog ate grapes before and was fine, so he’s not sensitive”No evidence for that. The toxic content varies between fruits, according to Merck.
“Tartaric acid is the proven cause”Proposed, not proven. The evidence is a six-dog case series and what is known about dogs’ kidneys.
“Blackcurrants are toxic to dogs”Not according to Merck, which says true currants (Ribes) have not been linked to kidney injury. Dried Zante currants are grapes and are.
“It’s too late to do anything after a few hours”Contradicted. The Dutch study found vet-induced vomiting still brought fruit up in most dogs at 4–12 hours.

Sources

Always confirm with your vet before acting on anything on this page.