Onion Poisoning in Dogs.


Unfortunately, onions are one of those definite No, No’s on the list of things dogs should not eat. Onion poisoning in dogs can be quite serious. Sometimes however, accidents happen. Bits of food can accidentally get dropped onto the floor where any canine dustbin can easily gobble it up.  If it’s a piece of cheese or carrot, all well and good, (who needs a vacuum anyway?). It is not good though, if the food item happens to be something dogs just should not have.

We often cook onions (and garlic) and I am notoriously bad at keeping things on the work surface, (as my dogs very well know). They tend to loiter when I am preparing dinner. Unfortunately, this happened to me recently.

I was busily chopping up onions to put in a vegetable soup I didn’t notice that a chunk flew off and landed on the floor. I only realised because I found the wayward onion slice in the next room a short while later. Floss, the collie had  swiped it up. Thankfully, she spat it straight out again.

How much onion would make my dog sick?

Thankfully, onions are not a favourite of dogs and they will usually spit them out straight away. According to experts, a dog would need to consume a considerable amount of onions to become sick.

Human foods, especially those containing onion are bad for dogs.

While other foodstuffs, like grapes for instance, can cause problems after the dog has consumed a small amount, onions at least, are a little less of hazard in small quantities.

All the same,  onions should be strictly avoided. It should also be noted that garlic, chives and leeks can, likewise, make dogs very sick.

Don’t forget as well – there are many other foods which contain onions and are equally as bad for dogs. Hamburgers, stuffing and many other types of food include onions.

Onions contain a compound called N-propyl disulfide which damages red blood cells.

Onions can build up enough in the dog’s system to become toxic which can potentially lead to hemolytic anemia.  This condition can destroy a dog’s red blood cells, leaving him without enough cells for normal body function.  In severe cases where the dog has consumed a lot of onions, or over a long period of time, the situation can be fatal.

As a general guide, here are some quantities of onion consumed, which depending on the size of dog, could be toxic:-

  • For small dogs around 10 lbs – 1/10th of a medium sized onion can be toxic.
  • Medium dogs around 30 lbs – 1/3rd of a medium sized onion could cause a toxic reaction.
  • Large dogs weighing around 60 lbs – 2/3rds of a medium sized onion.
  • If the dog already has kidney problems, consuming onion could be more serious still.

Symptoms of onion poisoning in dogs.

  • Vomiting.
  • Diarrhoea.
  • Dehydration.
  • Tender stomach.
  • Lethargy.
  • Breathing difficulties.

These symptoms may appear 24 hours after the dog has consumed onion, but can develop over a period of several days.

Treatment for onion poisoning.

  • Your vet may induce vomiting.
  • Re-hydration.
  • Medication to stop seizures.


In conclusion, it is best to keep onions completely out of reach of your pet, just in case. Remember too – there are many other products which contain onion, which your dog should not eat.

However, most dogs will recover well from the effects of consuming onions. Veterinary attention should be sought if you think your dog has eaten onions. For our article on toxic palm follow the link here.