Vitis vinifera fruits, including grapes, raisins, sultanas and currants, are not safe for dogs. Ingestion of even a small amount may lead to vomiting, diarrhea and kidney failure, which may occur several days after consumption.1 Not all dogs are affected by these fruits, and some believe that a fluoride-based pesticide called cryolite used on grape crops could be to blame.
However, some dogs have gotten sick even after eating organic or homegrown grapes, so it’s best not to take a chance and avoid feeding these to your dog. Plants of the genus allium, which includes onions, chives, garlic and leeks, are another category that can make some dogs sick.
If large doses are consumed, it can lead to drooling, abdominal pain, vomiting and diarrhea, which may not occur for several days after ingestion. Oxidative damage to red blood cells, causing them to risk rupturing, can also occur,2 as can weakness, rapid breathing, high heart rate, pale mucous membranes, reddish or brown urine and anemia.
That being said, in the case of garlic very large quantities are needed to be dangerous — much more than you would typically feed to your dog. Dogs can healthfully consume 1/4 teaspoon of freshly chopped garlic per 15 pounds of body weight and reap substantial health benefits, just don’t overdo it.