“Onion and garlic are not safe for dogs." (recipe card footer: "No onion, garlic or salt, not safe for dogs.")”

The veterinary toxicology record treats onion and garlic as toxic to dogs. Merck describes Allium species toxicosis as developing after ingestion of large amounts of plant material, with dogs and cats affected after eating raw, cooked, dehydrated or granulated onions and garlic, and clinical signs of acute hemolytic anemia including weakness, pallor, icterus and collapse appearing several days after ingestion. Merck lists garlic, onions, chives and leeks in the group, states garlic is 3 to 5 times more toxic than onion, and notes cats are the most susceptible species followed by dogs, with toxicosis most commonly associated with concentrated forms such as dehydrated flakes, powders or dry onion soup mixes. The mechanism given is sulfur-containing oxidants released by chopping, cooking and chewing and by gut microbes, which on absorption cause oxidative damage to red blood cells and Heinz body formation. The effect is dose-related and the published thresholds are for dogs specifically. The peer-reviewed review reports that dogs and cats are highly susceptible to Allium toxicosis and that ingestion of 5 g/kg of onions by cats and 15 to 30 g/kg by dogs is enough to cause clinically important hematologic changes. The dvm360 toxicology brief gives the same figures and adds that onion toxicosis is consistently noted in animals that ingest more than 0.5% of their body weight in onions at one time. The same review notes a study in which dogs given 5 g/kg of fresh garlic daily for seven days developed significant hematological changes including reduced hematocrit and hemoglobin and the appearance of Heinz bodies, although no clinical signs of anemia were observed. It also records that cooking, drying and processing do not eliminate the toxic compounds. Poison control and professional guidance is avoidance rather than a permitted amount. The ASPCA lists onion, garlic and chives together as Allium species on its people foods to avoid list. Pet Poison Helpline's Dr Ahna Brutlag states that from a toxicity perspective garlic is roughly 5 times more concentrated than onion, and that because of this an even smaller amount could lead to toxicosis, with as little as one clove capable of causing toxicity in cats and small dogs. AKC's garlic page states that research shows 15 to 30 grams of raw onion can cause adverse symptoms in dogs, that garlic is five times more toxic than onion, and that garlic powder and concentrated extracts are more dangerous because they pack more of the toxic compounds into a smaller amount. A separate consumer page citing VCA states that n-propyl disulfide is not affected by heat, so raw and cooked onions are both unsafe for dogs. There is an opposing position promoted by garlic supplement sellers and some raw-feeding outlets. One such page argues that most garlic warnings rest on the November 2000 American Journal of Veterinary Research study in which four dogs received 1.25 ml of garlic extract per kg daily by feeding tube for seven days, equivalent to about 5 g of whole garlic per kg, which it characterises as roughly 24 cloves a day for a 50-pound dog. A supplement brand page describes the same study's result as oxidative damage to a small percentage of red blood cells with no dog becoming anemic and no dog showing sickness or weakness, while noting researchers expected continued feeding to eventually cause anemia. These are brand and advocacy pages, and no peer-reviewed study was found establishing a safe long-term dietary dose of garlic or onion in dogs.