Garlic and onion belong to the plant species Allium. Garlic has been used by humans as a food flavoring, blood purifier, antibiotic, and antiparasitic drug.

Both garlic and onion can be toxic to dogs, cats, and other animals. Cats appear to be more sensitive than dogs. In dogs and cats, onions and garlic can cause a breakdown of the red blood cells, resulting in Heinz body anemia. The bulbs, bulbets, flowers, and stems of the garlic and onion can all be toxic. There are some human baby foods that have onion in them, and it is not recommended to feed them to pets. The very small amounts of garlic that are present in some commercial pet foods have not been shown to cause any problems.