Garlic is dangerous for dogs to eat because it can damage red blood cells, leading to serious health problems. It is part of the onion family, and all members of that family are toxic to dogs. However, garlic is approximately five times more potent than onions.
Dogs rarely eat enough raw garlic to cause health problems, but garlic poisoning from concentrated garlic products such as soup mix is more common. It can take several days for symptoms of garlic poisoning to appear, so owners of dogs who eat garlic should contact a veterinarian for advice even if the dog seems healthy. Symptoms of garlic poisoning include lethargy, drooling, digestive upset, weakness and abdominal pain.