Felis ISSN 2398-2950

Allium species poisoning

Contributor(s): Alexander Campbell, Patricia Talcott


  • A large plant group of mostly perennial bulbous herbs with characteristic aroma.
  • Group includes onion, spring onion, shallots, field garlic, garlic, chives, leeks, wild or wood garlic, crow or false garlic.
  • All parts of the plants should be considered toxic.
  • The onion (Allium cepa) is the most significant toxicologically in cats.
  • Signs: gastrointestinal effects, dehydration and subsequent development of hemolytic anemia and Heinz body formation.
  • Diagnosis: signs and case history.
  • Treatment: gastric decontamination if appropriate, with symptomatic and supportive care. Emphasis on addressing a potential hemolytic anemia.
  • Prognosis: fatal cases are rare.



  • Ingestion of plants or plant extracts.
  • Note that cooked plant material may still be hazardous.

Predisposing factors


  • Cats appear particularly susceptible to ingestion of plants from this group.


  • Hemoglobin in cats is particularly susceptible to oxidative denaturation. Splenic removal of Heinz body-containing red blood cells is very efficient in cats, and the presence of Heinz bodies does not always lead to a hemolytic event.
  • Heinz body formation has been reported in cats fed baby food containing onion powder.
  • A dosage as low as 5 g/kg BW may lead to hematological abnormalities.


  • The toxic mechanism has not been fully elucidated and probably multifactorial.
  • Toxins are thought to be a group of structurally similar disufides and thiosulfate compounds.
  • N-propyl disulfide depletes glucose-6-phosphate dehydrogenase (G6PD) within erythrocytes diminishing the protective effect of glutathione, as this remains in its oxidized state.
  • In this state glutathione forms mixed sulfide bonds with hemoglobin and precipitates within the cell resulting in the formation of Heinz bodies.
  • These affected cells are usually removed from circulation by the reticuloendothelial system, thereby inducing anemia.
  • There is evidence to suggest that there are other oxidative extracts within the plant material that may directly induce methaemoglobinemia and Heinz body formation.


  • Onset of signs is variable, although signs are usually apparent within 6-24 hours.
  • Signs of hemolytic anemia or methemoglobinemia may be delayed for 1-5 days.
  • Full recovery may take 7 days or more.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Robertson J E, Christopher M M & Rogers Q R (1998) Heinz body formation in cats fed baby food containing onion powder. JAVMA 212 (8), 1260-1266 PubMed.
  • Edwards C M & Belford C J (1996) Six cases of Heinz body haemolytic anaemia induced by onion and/or garlic ingestion. Aust Vet Pract 26 (1), 18-21 ResearchGate.
  • Miyata D (1990) Isolation of a new phenolic compound from the onion (Allium cepa L.) and its oxidative effect on erythrocytes. Jap J Vet Res 38 (2), 65 VetMedResource.
  • Solter P & Scott R (1987) Onion ingestion and subsequent Heinz body anaemia in a dog: a case report. JAAHA 23 (5), 544-546 VetMedResource.
  • Smith C H & Ellison R S (1986) Concurrent onion poisoning and haematuria in a dog. N Z Vet J 34 (5), 77-78 PubMed.
  • Kay J M (1983) Onion toxicity in a dog. Modern Veterinary Practice 64 (6), 477-478 VetMedResource.
  • Kobayashi K (1981) Onion poisoning in a cat. Feline Pract 11 (1), 22-27 VetMedResource.

Other sources of information

  • Burrows G E & Tyrl R J (2001) Chapter 47 Liliaceae. In: Toxic Plants of North America, Iowa State University Press, pp 752-756 ISBN 0-8138-2266-1.
  • Cooper M R & Johnson A W (1998) Poisonous plants and Fungi in Britain: Animal and Human Poisoning. 2nd Edition. The Stationery Office, London, pp 31-34 ISBN 0 11 242981 5.