Allium Toxicity in Dogs and Cats (Onion and Garlic Poisoning)
All {{Allium}} plants — onion, garlic, leeks, chives, and shallots — are toxic to dogs and cats because their organosulfur compounds oxidize red-blood-cell hemoglobin, producing {{Heinz body}} anemia. Toxicity applies to raw, cooked, and dehydrated forms and is dose-dependent.
Plants in the Allium genus — onion, garlic, leeks, chives, and shallots — are toxic to dogs and cats. Alliums produce cysteine-derived organosulfur compounds that give them their characteristic smell and flavor; in companion animals these same compounds are the source of poisoning. **Mechanism.** When allium tissue is crushed, chewed, or digested, it releases sulfur compounds that break down into oxidizing agents, principally N-propyl disulfide (related to thiosulfate chemistry). After absorption from the gut, these enter red blood cells and oxidatively damage hemoglobin. The denatured hemoglobin precipitates into inclusions called Heinz body bodies. The spleen and liver recognize the damaged cells and remove them (extravascular hemolysis); if enough cells are destroyed the animal develops Heinz Body Anemia in Dogs and Cats. **Dose and species sensitivity.** Toxicity is dose-dependent. Reported problematic doses are often cited around 15-30 g/kg of body weight for dogs, with cats more sensitive (as low as ~5 g/kg). Because a medium onion is roughly 150 g, a small dog can reach a meaningful dose from a fraction of one onion. Dehydrated and powdered forms (onion/garlic powder in seasonings, soup bases, and snacks) are more concentrated and easy to underestimate. Certain breeds with inherited red-cell traits (e.g., some Japanese breeds like Akita and Shiba Inu) are more susceptible. **Onset and signs.** In experimental studies, Heinz bodies appeared within a day of a single dose of dehydrated onion, peaked around day three, and packed cell volume fell over several days — so clinical signs are typically delayed and cumulative rather than immediate. Signs include lethargy and weakness, pale gums, elevated heart and respiratory rate, vomiting or diarrhea, and dark, reddish, or brown urine from hemoglobin breakdown. **Action.** There is no antidote; treatment is supportive (decontamination if recent, fluids, and transfusion in severe cases). Owners who suspect ingestion should contact a veterinarian or pet poison control rather than waiting for symptoms.