Verdict: No, toxic
Grapes and raisins are highly toxic to dogs and can cause acute kidney failure, even in small amounts. The exact toxic compound and mechanism are still unknown, and there is no established safe dose. If your dog ingests any amount of grapes or raisins, it is considered a veterinary emergency and immediate treatment is crucial.
The exact mechanism is not fully understood, but it is believed to cause acute kidney injury, possibly through a tartaric acid salt or other unidentified compound. It can lead to nephrotoxicity.
Unknown