Why are grapes and raisins dangerous to dogs?

The story behind the answer

Grapes and raisins can cause sudden kidney failure in dogs. The exact toxin isn’t fully confirmed, but tartaric acid (and its salt, potassium bitartrate) is a leading suspect. Toxicity is unpredictable—some dogs get very sick from a few grapes, while others don’t—so any amount is considered unsafe. Raisins are even more dangerous because they’re concentrated. Early signs include vomiting, diarrhea, lethargy, abdominal pain, and reduced urination.

Remember it this way: “Raisins ruin kidneys; grapes gut GFR.” It’s not an allergy, a sugar spike, or seed blockage—the kidneys are the target. If a dog eats grapes or raisins, contact a vet immediately; prompt treatment (often inducing vomiting and IV fluids) can be lifesaving. Avoid grape-containing foods like trail mix, cookies, and cereals.