Grapes are not good for dogs to ingest, and even small amounts of grapes or raisins can be fatal, according to PetMD. The exact reason for the toxicity is not known; however, the effects of the poisoning have been heavily documented.
Symptoms of grape poisoning in dogs include loss of appetite, vomiting, diarrhea, weakness, dehydration, stomach pain, passing little to no urine and kidney failure, according to PetMD. A dog with grape poisoning should have vomiting induced to rid its stomach of the grapes, and it should receive immediate medical attention. Do not induce vomiting if the dog is having problems breathing or is unconscious.