How Long Does It Take For Onions To Kill A Dog?

Has your dog eaten an onion? ¹,²

If you’re worried your precious dog just stole a hamburger from the dinner table, there’s no need to panic.

Even if the hamburger had onion in it, that won’t surely kill your pet.

However, it is important that you understand just how dangerous onions are for dogs.

The hamburger your dog just gulped down might give him an upset stomach, but if your pet eats a medium-sized onion he might be in serious trouble, particularly if you have a Chihuahua or some other type of small dog. 

In this article we’ll have an in-depth look at why onions are dangerous for dogs, how to recognize onion poisoning and what to do about it. 

Why are onions toxic for dogs?

If you eat an onion, your biggest problem will be a case of bad breath. If your dog eats one, his life might be in danger. 

Onions contain a chemical compound known as N-propyl disulfide, which the dog’s body cannot process.

The compound can cause extensive damage by attaching itself to oxygen molecules in the red blood cells.

Now, if the red blood cells fail in their primary mission of transporting oxygen to tissues and organs, the dog’s immune system will start treating those cells as an invader.

Whenever there’s a bacteria or a virus in the organism the immune system attacks them, and that’s usually a good thing.

But, it the immune system starts destroying red blood cells in a process called hemolysis this will result in hemolytic anemia, and this can be lethal to your dog.

What parts of the onion are dangerous to a dog?

Basically all parts of the onion are toxic to dogs, flesh, leaves and the juice. It doesn’t matter if the onion is cooked or raw, the toxic compound is still present.

Another danger many people ignore is the onion powder, which may be present in lots of foods you may buy at the supermarket.

The concentration of N-propyl disulfide is higher in onion powder than in the raw onion. Canned foods, soups or sauces, all may contain onion powder, which is why you should always read the labels carefully before serving your pet any type of processed food. 

What are the main symptoms of onion toxicity?

If your dog ate some food containing onions, you need to look out for any symptoms that he is suffering from onion poisoning.

As mentioned above, one hamburger is unlikely to cause serious issues, but if you are not sure how much onion did the dog ingest you have to monitor him carefully. Don’t wait till your pet starts feeling really bad. 

Let’s have a look at the main symptoms of onion poisoning:

  • Lethargy
  • Weakness
  • Decreased appetite
  • Pale gums
  • Fainting
  • Reddish urine
  • Vomiting
  • Elevated heart rate
  • Excessive panting

If you know he’s been raiding the pantry and might have eaten something containing onions, take him to the vet as soon as you notice any worrying sign.

On the other hand, if you caught your dog in your vegetable garden eating onions, don’t wait at all.

The sooner he gets medical attention, the higher the chances he won’t suffer serious consequences. 

How long does it take for the symptoms to appear?

It might take a full 24 hours for the toxic compound in onion to be fully absorbed in the system. At the same time, it might take 72 hours for the toxin to start wreaking havoc in your dog’s blood. This gives you plenty of time to get to the vet and take steps to prevent major tissue and organ damage caused by the lack of oxygen. 

Another thing to keep in mind is that the ill-effects of onion accumulate over time. If the dog ingests a moderate quantity of onions several days in a row he might develop the same level of toxicity as that generated by eating a few full onions at a time. 

How much onion can kill a dog?

According to experts a dog can safely eat up to 0.5% of their body weight in onions before they start showing signs of poisoning. If you have a 30lbs dog, eating up to 2.5 ounces of onion won’t cause serious problems, but anything above that will put his life at risk. Keep in mind that a small onion measuring 1-2 inches in diameter weighs 2.46 oz on average. Note this is the average weight and some onions can weigh as much as 5.3 oz, which is way above the safety limit. 

What can I do if my dog ate onions?

If you have reason to believe your pet ate a couple of onions or indeed any amount above the safety limit, you should call your vet right away. If you cannot get hold of your vet, you can try to induce vomiting. That only works if the dog just ate and the onions might still be in his stomach. If he stole some food containing onions hours ago, it has already been digested and has moved on to the intestines, so there’s no point in making the dog vomit. (Food spends an average of two hours in the dog’s stomach.

Another thing you can do is give your dog activated charcoal to counter the ill-effects caused by the toxic compound in onions. Activated charcoal for dogs is available in various forms, such as liquid, capsules, tablets or powder. It’s always a good thing to have some charcoal in your medicine cabinet if you have dogs as it can be used for emergency treatment for various types of toxins. 

However, these are emergency measures you can take, but you still need to have your pet checked out by a professional as soon as possible. 

How is onion poisoning treated?

The vet will examine your pet and probably order some blood tests to see if the toxic compound is already interfering with the red blood cells. If the tests show that he has developed hemolytic anemia, your dog will probably require a blood transfusion. If that is the case, your dog might need to spend the night in the hospital for observation. Once he is discharged, it is recommended that he rest as much as possible. He doesn’t need any excitement or long walks. Taking him outside to do his business and put him back to bed. Your dog might need to have another blood tests after a few days, so the vet can evaluate the red blood cells count to see if it’s back within a normal range. 

The good news is that with immediate medical treatment, your dog will make a full recovery. Once there’s no more N-propyl disulfide in his system, the bone marrow will start producing new blood cells and your pet will be back on his feet in a couple of days.

Are some dogs more susceptible to onion poisoning?

Onions are toxic to all dogs, and cats for that matter. However, there are studies indicating that certain breeds of Japanese descent are more prone to develop serious side effects after eating onions. These breeds include Akita, Shiba Inu and the Japanese chin.

What other vegetables are toxic to dogs?

All the plants in the Allium family, which includes onions, garlic, chives and leeks, are toxic to dogs. Garlic is even more dangerous for dogs. According to studies, it takes 15-30 grams of garlic per kilogram of body weight to cause damage to the dog’s red blood cells. The average garlic clove weighs 3-7 grams so a dog would have to eat quite a lot of it to be in any real danger. On the other hand, you have to be very careful with garlic powder. Many people use garlic powder to season their dishes and it can also be found in many processed foods, but one spoonful of garlic powder contains the same amount of toxin as several cloves.

What are some dog-friendly vegetables?

A dog needs some vegetables in his diet, to get enough vitamins and minerals. Carrots and sweet potatoes are a great source of vitamins, and, of course, you can give your dog various types of fruit, such as apples, bananas or berries. 

There’s no reason not to give your dog some meatballs or a nice hamburger, as long as you make sure there’s no onion or garlic in them. This will require a bit of home cooking, but you can prepare some delicious meatballs for your dog by substituting onion and garlic with shredded carrots and cheese. Not a lot of cheese though, as too much salt is also bad for a dog.

Closing thoughts

Onions are toxic to dogs and should be avoided at all costs. If your dog manages to get a few bites of some food containing onions, there’s probably no need to panic, but if he’s eaten a lot you should have him checked by a vet as soon as possible. Even if the dog seems just fine at the moment, keep in mind that onion toxicity might take anywhere between 24 and 72 hrs to develop. But, with adequate medical care the prognosis is excellent as onion poisoning is rarely fatal. 

Photo credits

¹ Clock photo by insung yoon on Unsplash

² Onion photo by Mockup Graphics on Unsplash

Sarah Pulsen

Hello, I have been in love with dogs since I was a little girl. I became even more infatuated with them when I was told by my Mum that I couldn't own one. Since I left home there has rarely been a time in my life when I have lived without a dog. My current dog is a Collie Terrier cross, called Ian.