- Allium — damages red blood cells
- Often delayed 1+ day
- Affects: Red blood cells
Why this verdict for cats
Leeks are highly toxic to cats, which are very sensitive to allium vegetables. Never feed them.
Warning signs to watch for
- Weakness
- Pale gums
⚠ If your cat ate leek
Act immediately — don't wait for symptoms.
- Call your vet or a pet poison helpline right away.
- Note how much was eaten and when.
- Do not induce vomiting unless a professional tells you to.
Leeks are the quiet member of the onion family, and by weight they are among the most potent. Because they are usually cooked into soups, stocks and gratins rather than served whole, the exposure is often larger and less obvious than a stray slice of raw onion.
How much is safe?
There is no safe serving for dogs or cats, and cooking does not reduce the toxicity at all — the compounds survive boiling, roasting and drying. As a rough benchmark for the allium family, damage becomes likely once a pet eats around 0.5% of its body weight in onion-equivalent, which for a 10 kg dog is roughly 50 g. Leek is at the stronger end of the family, so it takes less. Cats are considerably more sensitive than dogs.
What happens if a cat eats too much?
Alliums attack red blood cells, causing what vets call Heinz body anaemia — the cells are damaged and then destroyed by the body. The catch is timing: signs usually appear one to five days after the meal, not immediately. Watch for weakness, unwillingness to exercise, pale or yellowish gums, rapid breathing, a fast heart rate, and urine that looks orange, red or brown. There may be a bout of vomiting or diarrhoea early on, then apparent normality before the anaemia declares itself.
⚠ What to do if your cat ate leek
Call your vet or a poison line with your pet's weight and how much leek was eaten (ASPCA 888-426-4435 · Pet Poison Helpline 855-764-7661). Do not wait for symptoms — by the time gums are pale, a significant fraction of red blood cells is already gone. If it was recent, decontamination may be worthwhile; after that, the plan is usually a blood check at 24 hours and again a few days later to catch the anaemia as it develops.
⚠️ Worried your pet got into this?
Frequently asked questions
My dog ate leek soup, not raw leek — is that safer?
No. The toxin is not destroyed by cooking, and soups and stocks often contain onion and garlic too, which stack the dose.
One small piece a few days ago — is it too late to call?
It is still worth calling. A blood test can show whether red cells are being affected, and treatment for anaemia is far easier before a pet becomes weak.
More vegetables for cats
By the CanMyPet Editorial Team · Reviewed against ASPCA Animal Poison Control, the American Kennel Club (AKC) and Pet Poison Helpline · Last updated July 31, 2026.
Sources
- ASPCA — People Foods to Avoid Feeding Your Pets
- American Kennel Club — Dog Nutrition
- Pet Poison Helpline — Poison List