How many grapes can my dog eat?
None, it’s as simple as that.

What to do if your dog eats a grape:
Call your vet immediately! Veterinarians can induce emesis (vomiting) within 2 hours of ingestion. If it’s been longer than two hours, it’s still recommended to bring your dog in for monitoring and to watch out for clinical signs of toxicity.

Why?
Although some dogs are reported unaffected, ingestion of grapes can and has led to acute kidney failure. Only recently have the mechanisms for toxicity of grapes been discovered. The Animal Poison Control Centre believe the tartaric acid which is what cream of tartar is made from, and potassium bitartrate found in grapes to be the culprit. The levels of these factors may vary depending on grape type, growing conditions, and ripening. Meaning the amount ingested to lead to acute kidney failure is unclear with doses between 20 to 150 mg/kg are reported as leading to nephrotoxicity1. Although a study published in the Journal of Small Animal Practice found that dogs following ingestion of grapes were more likely to develop gastrointestinal tract clinical signs and that symptomatic kidney injury is much rarer, the induction of emesis (vomiting) within 12 hours remains highly warranted2.

What are the signs of grape toxicity?
One or more clinical sign may occur: vomiting, diarrhoea, abdominal pain, lethargy/weakness, increased water consumption and tremors. These signs usually present within 12 hours of ingestion, but a careful eye should be kept for at least 24 hours.

What about raisins, dates, or other similar foods?
Raisins and natural grape jams are just as toxic as grapes themselves. However, some jams and juices go through a process of detartrating which removes excess tartrates (the toxic component) to preserve flavour and appearance, in this case ingestion may not lead to toxicity.
Dates are safe for dog consumption, just watch out for date pits as they can cause obstructions.
Raspberries, blackberries, blueberries, and strawberries are also safe for dogs to eat.

References

  1. Dujowich. Letter to the Editor – Unique sensitivity of dogs to tartaric acid and implications for toxicity of grapes. Journal of the American Veterinary Medical Association 2022;258:706-707.
  2. Dijkman M, van Roemburg R, De Lange D, Hugen S, Robben J. Incidence of Vitis fruit‐induced clinical signs and acute kidney injury in dogs and cats. Journal of Small Animal Practice 2022.