Onions, Garlic, Chives, Leek Plants (Allioideae)
Leek plants such as onions, garlic, chives, and leeks are among the most popular ingredients in human cuisine. However, many pet owners do not know that these very foods can be highly toxic to dogs and cats. Even small amounts—whether raw, cooked, or dried—can cause serious health problems. It is particularly problematic that the symptoms of poisoning often appear only after a delay. In many cases, leftovers of seasoned foods, such as onion sauces or garlic bread, are offered as supposed treats—with potentially life-threatening consequences.
The most important facts at a glance
Onions, garlic, and other members of the Allioideae family are highly toxic to dogs and cats. The damage is caused by oxidative processes in red blood cells, which can lead to hemolytic anemia and, in severe cases, death. Since symptoms often appear with a delay, early veterinary treatment is crucial. The prognosis varies depending on severity, animal species, and reaction time. Conscious avoidance of these plants in pet nutrition is essential.
Causes, development and progression
All leek plants are potentially toxic to dogs and cats.
The responsible substances are a group called propyl disulfides.
These sulfur compounds appear to be readily absorbed through the gastrointestinal tract and then converted into highly reactive oxidizing agents.
Cooking, drying, and similar processes do not alter their effect.
The most common cause of poisoning is the unintentional feeding of foods containing ingredients from the Allium family. Particularly insidious: dried, powdered, or cooked forms also retain their toxic effect. However, animals can also ingest these substances from dropped leftovers, garbage bag contents, or compost piles. In some cases, garlic is deliberately used as a natural remedy for parasite control—which, from a veterinary perspective, is not only ineffective but dangerous.
Mechanism of action
Organosulfur compounds oxidize the blood pigment hemoglobin in red blood cells to methemoglobin, followed by associated instability of red blood cells and increasing hemolysis (dissolution of red blood cells). This results in anemia (blood deficiency).
Some dog breeds, such as the Akita Inu and Shiba Inu, are particularly susceptible to oxidative damage caused by onions due to genetically determined peculiarities in their erythrocytes.
Cats, whose red blood cells are already very susceptible to oxidation, also react sensitively.
The toxic dose for onions is already reached in dogs with an intake of 15 to 30 g/kg body weight and in cats with 5 g/kg body weight.
The toxic effect of leek plants is based on organic sulfur compounds. Specifically, N-propyldisulfide, allyl propyl sulfide, and thiosulfates attack red blood cells (erythrocytes). These substances cause so-called oxidative stress in the cells, lead to the formation of Heinz bodies—which are degenerated hemoglobin structures—and ultimately cause the destruction of erythrocytes (hemolysis). As a result, severe anemia (blood deficiency) can occur, which severely impairs oxygen transport in the body. Additionally, methemoglobin can form—a form of hemoglobin that can no longer transport oxygen.
Symptoms of intoxication
Symptoms of intoxication begin one day or sometimes even several days after ingestion.
The primary symptoms to observe are:
- Loss of appetite
- Vomiting,
- Diarrhea
- Bauchschmerzen
- Anämie
- Pale or jaundiced (yellow) mucous membranes
- Weakness
- Increased heart rate
- Increased respiratory rate
- Hemoglobinuria (dark urine due to hemoglobin excretion)
- Presence of Heinz bodies (clumps of blood pigment) in erythrocytes
Death occurs due to lack of oxygen.
Diagnosis
For diagnosis, a precise anamnesis is crucial: When and in what quantity was a leek plant ingested? In addition, blood and urine tests provide important clues:
- The blood count often shows regenerative anemia with increased reticulocytosis.
- Specific is the detection of Heinz bodies using dyes such as brilliant cresyl blue.
- In blood chemistry, elevated liver enzymes and bilirubin levels may be detectable.
- Urine analysis can detect hemoglobinuria (free hemoglobin in the urine).
Imaging procedures are generally not necessary but can help rule out other causes in cases of unclear symptoms.
Therapeutic principles
There is no antidote. Antioxidants (Vitamin E and Acetylcysteine) can be used. Therapeutic measures vary depending on the amount ingested and the animal’s clinical condition. If ingestion was recent and no symptoms are present, immediate decontamination of the digestive tract is performed by emptying the stomach and intestines. This means inducing vomiting and administering activated charcoal to prevent further absorption of toxins. Decontamination should ideally occur within 2 hours of toxin ingestion. Plant parts sometimes remain in the stomach for a longer time, so inducing vomiting or gastric lavage may still be useful at a later point.
In symptomatic cases, intensive symptomatic and supportive therapy is required:
- Intravenous fluid therapy to stabilize circulation, improve renal blood flow, and promote hemoglobin excretion
- Oxygen administration for severe anemia or methemoglobinemia
- Blood transfusion for severe hemolysis or if clinical symptoms indicate significant hypoxia
- Administration of antioxidants such as N-acetylcysteine to reduce oxidative cell damage
All measures should be closely monitored and accompanied by repeated blood count checks.
Prognosis & follow-up care
The prognosis is generally good. It heavily depends on the time of diagnosis, the amount of toxin ingested, and the animal’s general condition. Mild to moderate poisonings with early treatment usually proceed without complications. In severe cases with strong hemolysis, however, the prognosis can be guarded to poor—especially if accompanying organ dysfunctions such as liver insufficiency occur.
Follow-up care includes regular blood count checks for at least one week, possibly longer. Full recovery can take up to 14 days. Owners should be informed about the risk of relapse with repeated ingestion.
Research outlook
Despite the well-documented toxicity of leek plants in dogs and cats, there are still some open questions in research that are important for veterinary practice:
Molecular biological mechanisms in detail:
Although it is known that sulfur compounds such as N-propyldisulfide trigger oxidative stress in erythrocytes, the exact molecular signaling pathways through which Heinz body formation, membrane damage, and apoptosis occur have not yet been fully elucidated. Further studies could contribute to the development of targeted antidotes.
Interindividual sensitivity:
The pronounced individual variability in sensitivity to Allium toxins suggests that genetic factors or differences in antioxidant capacity play a role. Future genetic or metabolomic analyses could help assess risk.
Different toxicity depending on Allium species:
There are indications that garlic is more toxic than onions due to higher concentrations of thiosulfates. Nevertheless, comprehensive quantitative comparisons of the toxicity of different Allium species in relation to dogs and cats are lacking.
Optimization of diagnostics and therapy:
The development of faster diagnostic tests for the determination of Heinz bodies or cellular oxidation markers in clinical practice could improve early diagnosis. The therapeutic efficacy of new antioxidant combinations (e.g., N-acetylcysteine, vitamin E, S-adenosylmethionine) is also currently being further investigated.
Education and prevention:
Despite increasing awareness of the issue, pet owner education remains insufficient. Future research projects in the area of behavioral and consumer analysis could help develop effective prevention strategies to reduce poisoning by Allium plants.
Frequently asked questions (FAQs)
1. From what amount are onions dangerous for dogs?
As little as 5 g/kg body weight can cause symptoms – about half an onion for a 10 kg dog.
2. Are cooked or dried onions less toxic?
No. The toxic compounds remain active even after heat treatment or drying.
3. Are small amounts of garlic harmless for tick prevention?
No. This practice is not evidence-based and can be harmful to health.
4. What symptoms appear first?
Symptoms often begin with apathy, vomiting, and dark urine within 24–48 hours.
5. Can onion poisoning be reliably diagnosed by blood test?
Yes. Heinz bodies in a blood smear and regenerative anemia are typical findings.
6. What to do if my dog has eaten onions?
Seek veterinary help immediately. Do not use home remedies.
7. Why are cats more sensitive?
Their red blood cells are particularly susceptible to oxidative damage, and they lack an effective detoxification system.
8. Can symptoms be treated at home?
No. Professional medical care is essential.
9. How long does recovery take?
Full recovery can take up to two weeks, depending on the severity of the poisoning.
10. Can animals get sick from onions multiple times?
Yes. Sensitivity persists, and even small amounts can cause damage again.
Literature
- Cope, R. B., 2005. Allium species poisoning in dogs and cats. Veterinary Medicine, 100(6), pages 428–432.
- Gwaltney-Brant, S., 2012. Allium species toxicosis in dogs and cats. Vet Clin North Am Small Anim Pract, 42(2), pages 373–382. Available at: https://doi.org/10.1016/j.cvsm.2011.12.007.
- Handl, S. and Iben, C., 2008. Food toxic to small animals – a literature review. Vet. Med. Austria / Wiener Tierärztliche Monatsschrift, 95, pages 235–242.
- Koyama, K., Fujita, Y., Inoue, K., Nakaoka, R., Okita, M. and Tsuchitani, M., 2006. Hemolytic anemia in dogs and cats induced by garlic. Journal of Veterinary Medical Science, 68(2), pages 165–171.
- Lee, J. A., Yamato, O., Tajima, M., Kuraoka, M., Omae, S. and Maede, Y., 2000. Onion toxicity in dogs: a retrospective study. Australian Veterinary Journal, 78(6), pages 434–436.
- Löwe, G. and Löwe, O., 2021. Poisoning in Dogs and Cats – A Veterinary Guide. 2nd edition. Kreuztal: Kynos-Verlag. 208 pages.
- Müller, M., 2019. Oxidative damage from leek plants: An underestimated risk for dogs and cats. Vet Journal, 33(5), pages 220–226.
- Vetpharm – Toxicological Database of the University of Zurich. Plant data sheet for Allium species. Available online at: https://www.vetpharm.uzh.ch/giftdb/pflanzen/0049_tvm.htm.