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Onions
Onions
Onions (Allium cepa) are severely toxic to cats. All Allium species — including onions, garlic, chives, and leeks — contain organosulfur compounds that oxidise feline haemoglobin, forming Heinz bodies and triggering haemolytic anaemia. All forms are equally dangerous: raw, cooked, powdered, or dehydrated onions. Onion powder is especially hazardous due to its high concentration.
Important Notes
Toxic compounds: N-propyl disulfide and organosulfur compounds (alk(en)yl cysteine sulfoxides); all forms toxic
Mechanism: oxidative damage to haemoglobin creates Heinz bodies; the spleen destroys affected red blood cells, causing haemolytic anaemia
Symptoms: lethargy, weakness, pale or yellowish gums, rapid breathing, loss of appetite, reddish-brown urine; onset often delayed 3–5 days
Onion powder in baby food, broths, gravies, or prepared meals is a common hidden source of toxicity
Never share any onion-containing food with cats; contact your vet immediately if ingestion is suspected
Potentially Toxic Parts
Powder
Raw form
Cooked form
Possible Symptoms Reported in Cats
Tachypnea, Dyspnea, and Cyanosis
Respiratory · Several days after ingestion
Collapse and Death
Cardiac · Within 24 hours (with massive doses) or several days after ingestion
Lethargy, Weakness, and Depression
Neurological · After a lag of several days (typically 3–5 days)
Pale or Icteric Mucous Membranes (Jaundice)
Gastrointestinal · After a lag of several days (typically 3–5 days)
Tachycardia and Heart Murmur
Cardiac · Several days after ingestion
Hemoglobinuria (Dark Urine)
Gastrointestinal · Several days after ingestion (typically 3–5 days)
Hypothermia and Cold Sensitivity
Neurological · Several days after ingestion
Vomiting, Diarrhea, Abdominal Pain, and Loss of Appetite
Gastrointestinal · Within 1 day (or delayed up to 2–4 days)
Disclaimer: This summary was compiled from multiple sources and is for informational use only. It is not a diagnosis or treatment plan. Toxicity can vary based on the substance, amount, plant part, and individual cat. If you think your cat may have been exposed to a toxic substance, contact a veterinarian right away.