The Dangers of Onion Toxicity

The organosulfoxides (sulfurs) in onions, garlic, leeks and chives react with the cell membranes of the red blood cells of dogs, causing the cells to lyse (explode).  Cats are even more sensitive to the lytic effects of  allium (onion family) toxicosis than dogs.

It is a common myth that a small amount of onions or garlic is not harmful to dogs.  In fact, many homemade dog treat recipes include garlic powder as a flavoring because dogs tend to love it so much.  Dogs are more tolerant of garlic than onions, and small amounts of either often do not produce effects that are noticed.

foxy roxy

Foxy Roxy - recently adopted from Nebraska Humane Society. Smaller dogs are more greatly affected than larger dogs by the same amount of onions.

However, I believe that any amount of garlic or onions is unacceptable, because it always causes damage on a cellular level, whether or not we notice the effects of the damage and label it “toxic.”

common definition of veterinary toxin – taking in a substance at a high enough level to cause measurable damage or issues that are noticed by others

correct definition of toxin – poison

A small amount of garlic or onion ingestion will cause a small amount of subclinical hemolysis.  That is, a small amount will cause a small amount of red blood cell explosion.  Dogs need their red blood cells to oxygenate their brains and other important organs.

A moderate amount of garlic or onion ingestion will probably cause your pet to feel light headed and lethargic, which may go unnoticed.

A large amount of garlic or onion ingestion will cause clinical signs that are felt by the dog and noticed by the people.  Signs may take several days to develop.   Signs include:

  • abdominal pain
  • vomiting
  • diarrhea
  • lethargy
  • fast heart rate
  • fast breathing
  • anemia – low levels of red blood cells
  • paleness secondary to anemia
  • icterus – yellowing of the skin, gums or whites of the eyes, in this case secondary to hemolysis

hem/o – blood

lysis – rupture or destruction

hemolysis – rupture or destruction of red blood cells

anemia – low levels of red blood cells

Heinz bodies – microscopic changes to red blood cells seen with this particular toxicity as well as some others.  Heinz bodies are little swellings seen on the cell membranes of red blood cells before they lyse.  They are signs of a weakened cell membrane.

Onion and garlic toxicity are rarely fatal, but they can cause serious illness secondary to the red blood cell destruction and resulting anemia that they cause.  The anemia caused by onion toxicity is a regenerative anemia, meaning the body will be triggered to make new red blood cells.  This process can take up to a week to begin, and until then, cell damage continues to occur.

If your pet has ingested onions, garlic or foods containing either, call your veterinarian right away.  At early stages, the toxicity can often be treated with supportive care and detoxification.  At later stages, oxygen therapy and blood transfusions are sometimes required along with supportive care and monitoring of anemia.

Please, even if the treat recipe says to add garlic, even if your dog loves leftover stew with onions, even if he has worked hard for the leeks he dug from the garden, never allow your dog to ingest foods from the onion family.  The resulting toxicity is rarely fatal, uncommonly dangerous, sometimes uncomfortable, but always occurs.


  1. Kathryn says on  06/18/2012 at 3:44 pm

    i heard grapes and brocolli are not good either, is that right? x

    • Grapes and raisins (dried grapes) are toxic. Broccoli gives them gas, but I’ve never heard of broccoli being toxic.

  2. c’est bon à savoir

  3. poor thing

  4. Lana says on  06/18/2012 at 3:45 pm

    I didn’t know about garlic ! Always gave it to the dogs, won’t any longer

  5. Michele L says on  06/18/2012 at 3:45 pm

    Grapes for sure…never heard brocolli before

  6. Michele L says on  06/18/2012 at 3:46 pm – check out this page, it has a full list

  7. wow never knew that. my dog eats onions all the time. he loves lettuce onions and tomatoes.

  8. Lisa says on  06/18/2012 at 3:47 pm

    SO SAD!

  9. Jerrie says on  06/18/2012 at 3:48 pm

    chocolate,sugar is also bad for them

  10. thank you..i always thought garlic was ok.

  11. When our dog was three months old, we dealt with this! It was awful, but he is fine now. Our vet was awesome!!!

  12. Poor pups, need to get the word out!!

  13. Jennifer says on  06/18/2012 at 3:53 pm

    broccoli is fine for dogs….grapes, citrus fruits, avocados, onions, garlic, chocolate, raisins can be deadly. other foods that aren’t good for them are: high fatty foods (french fries, donuts), foods with corn, wheat and yeast, high sugary foods and soda.

  14. Kristian says on  06/18/2012 at 3:53 pm

    You just can’t tell that too often!

  15. I’ve asked three different vets about using a half teaspoon of granulated garlic in a batch of dog treats (yield 120 treats) and have been told that such a small amount isn’t harmful.

  16. Deborah says on  06/18/2012 at 3:54 pm

    Let’s feed our kids what’s good for THEM!

  17. Vesna says on  06/18/2012 at 3:55 pm

    ne mogu to ni čitati ” užs !

  18. Ladin says on  06/18/2012 at 3:55 pm

    And (bell) peppers are also very dangerous! I had one day some left overs and i put some in her bowl. The whole night my dog got sooo sick, i thought she was dying :(

    • I make our dogs their own very small salads when I make ours. They get diced pieces of broccoli, green and red peppers, lettuce spine, plus shredded carrots and shredded zucchini. They’ve never gotten sick from any of that. We had a dog with kidney failure and I ended up having to make all of her meals. Broccoli was one of the main recommended ingredients.

    • Anonymous says on  01/21/2014 at 3:56 am

      Bell peppers are not toxic to dogs.

  19. poor fellow (:

  20. Karen says on  06/18/2012 at 3:56 pm

    Is that raw or cooked or both? Koli loves bolognaise but it contains both

  21. My dog George “counter surfed” and ate a whole avocado, skin and all. We didn’t discover it until I was preparing the guacamole and noticed I was one avocado short. We panicked and called the vet, but it turned out fine. However he is a BIG boy so at over 90 pounds he can get away with eating bad things.

  22. shared

  23. Yes it happend to a freind of mine, sharing spagetti sauce. Almost lost their girl. They were devesated.

  24. Thank you! I’m always telling my mom this and she never believes me that dogs should not eat food with onion in. Now if I show her this she’ll believe me!

  25. Thank you for sharing this valuable information.

  26. Nicele says on  06/18/2012 at 4:02 pm

    Oh no!! My 13lb dog loves grilled onions as an occassional treat, he will be sad to know he can’t have any more :(

  27. Maybe it varies, but my dog was chewing on what I thought was a stick outside (not everyone lets them do that, but please don’t judge!) and it turned out to be connected to a vine in the grape vine family? My poor dog was sick for hours, all night. Grapes & vines are another toxin for dogs!!

  28. OMD!!!! My food from THE HONEST KITCHEN contains garlic!!!!

  29. I truly had no idea.

  30. Helen says on  06/18/2012 at 4:07 pm

    Please, get the veterinary facts before deciding on what you should and shouldn’t feed. Garlic, onions, and chives also have that effect on humans in very large doses. Onions are the most worrisome in dogs, but most large dogs will tolerate a little onion without issue. Garlic is rarely a cause for concern. In fact, it is frequently used as a natural pest repellent. Large dogs don’t seem to have issues. As far as broccoli, it, along with other cruciform veggies like cauliflower can cause excess gas so owners of dogs who may be prone to bloat should be careful about feeding it. The veggie itself is not dangerous. Grapes and raisins are absolutely a no no. They have been found to cause acute renal failure, sometimes irreversible.

    • donna says on  06/18/2012 at 9:13 pm

      I had heard how bad grapes are- but not until after feeding them to my dogs for their whole lives-both were largish boys,( shar-pei & mastiff X) and lived till 16 & 18 yrs. One loved grapes and begged for them- he would have eaten many,many kilograms of grapes in his 16 yrs.

      • Anonymous says on  01/29/2013 at 7:22 pm

        my dog loved grapes also, he thought they were small balls and played with them for an hour before he ate them. Lived to 15. Like people, it probably depends upon the dog such as people with peanut allergies, but wouldn’t want to take the chance now.

    • Right, Helen. When I make the salads for the dogs, they get a very minimal amount of small diced pieces of broccoli. I hadn’t considered bloat as a possible consequence of the cruciferous veggies. Our dogs are large and the salads are small, primary ingredients are the shredded carrots and shredded zucchini. They don’t get any leftovers from our meals.

  31. grapes arent toxic for my dog…

  32. Marie-José says on  06/18/2012 at 4:08 pm

    is this true?! a lot of people feed garlic pills to there dogs and cats to keep the flees away!

  33. I am allergic to alliums (except garlic) myself, so they are never in the house, thankfully, since my dog must taste everything that I eat.

  34. Our vet told us that it could be a small piece of onion, onion skin, or green onion tops…. We had one sick puppy. He just happened to get a piece that fell on the floor while we were making soup. I’m very careful now!!!

  35. You can probably get away with it but I always wonder why? Maybe because one of our dogs has an auto-immune issue, but I never feel like finding out that she can or can’t eat onions/grapes/chocolate the hard way – what am I proving!?

  36. Brigada pela dica!!!!

  37. Can somebody tell me why grapes have never effected my dog?(in a message)

  38. I had a friend who had a German Shepard puppy and the little girl next door fed him chocolate through the fence and he died. Was so sad. The people felt terrible that had no idea she did that. She was only about

  39. 3 years old so she didn’t know any better.

  40. Opal says on  06/18/2012 at 4:26 pm

    My JRT, Lucy accidentally got 1 small piece of cooked onion. She got so deathly ill. She threw up over & over again & again. When her little tummy was empty, she still kept throwing up, exhausted between bouts. Finally resting, shaking & chilled. It was horrible. She was about 8 months old. When I heard garlic can do the same thing, I am very careful handling it in the kitchen. They say some garlic is ok. But don’t know how much. It’s in some of their dog food.

  41. another important one!

  42. does that do the same cooked or raw?????? or both????no more tablescrapes.

  43. Scott says on  06/18/2012 at 4:32 pm

    thank you for that information scotty

  44. Sharon says on  06/18/2012 at 4:36 pm

    OMG !!! My bloody vet TOLD me to put a small amount of garlic in my pups food to help stop any fleas. She has just turned 1 and luckily she has had no reaction to it. She gets no more and i’m changing vets asap.

  45. Annette says on  06/18/2012 at 4:41 pm

    More people need to know this. Onions, garlic and grapes/raisins are toxic to dogs even in small doses.

  46. Vicci says on  06/18/2012 at 4:45 pm

    I give my dog a few times a week a little bit of garlic in his food against the flees. When I told the vet he said this is an old but good remedy and never mentioned this is bad. I do this for about a year now and the dog was never sick. And he’s medium size, about 15kg.

  47. Julie says on  06/18/2012 at 4:50 pm


  48. Tami says on  06/18/2012 at 5:09 pm

    Thank you for sharing this – I had no clue!!

  49. Angela says on  06/18/2012 at 5:09 pm

    BROCCOLI: There has been a bit of confusion where broccoli is concerned. Broccoli is very good for dogs, however, if the daily intake exceeds more than 10% of the animals diet – problems can occur. The toxic substance is isothiocyanate and can cause gastrointestinal irritation.
    NOTE: Broccoli toxicity was first noted in dairy cattle raised in California. When there was an over abundant broccoli crop, it was fed to the cattle. Problems may have occurred because cattle have rumens and digest things much more thoroughly, therefore taking in more of the toxic substance.

  50. Angela says on  06/18/2012 at 5:10 pm

    My service dog Sweetpea got really sick from sneaking some greenbean casserole once. She was horribly sick and ended up needing fluids and several meds. It took her about 2 weeks to get over it.

  51. Lizzy says on  06/18/2012 at 5:28 pm

    Unless you’re shoving whole cloves of garlic down your dog’s throat, garlic is fine. Many pet foods have garlic. And I don’t mean some mess you find at Wal-Mart. Top shelf dogs foods like The Honest Kitchen have formulas that contain garlic. I have 5 dogs who all eat food containing garlic. They’re perfectly healthy and they have no problems with fleas and ticks. I’m also not sure why there’s such a big fuss over Avocados either. There’s an entire dog food line based on Avocados called Avo-Derm. It’s even made Whole Dog Journal’s best foods list.

  52. I feel like a broken record saying this again, but garlic is fine in small quantities. It is in a LOT of things the average joe buys for their dog. In fact, if you buy canned food, it very well may be in that. Garlic is only toxic in large quantities. For it to be toxic to a dog, a five lb dog would have to consume about 5 cloves in one day. Who goes around giving their dog garlic by the cloves? Do it by the tsp (the powder form) and it is not toxic. The misinformation that it IS comes from the fact that onions are. While they ARE in the same family and onions ARE toxic in any dose, the same is NOT true of garlic.

  53. Sharon, no need to change vets. The vet was right, not right. Once again, garlic being toxic in small quantities is misinformation.

  54. *not wrong*

  55. Vicki says on  06/18/2012 at 5:51 pm

    That is good to know!

  56. Sharon says on  06/18/2012 at 6:06 pm

    Brianna, thankyou for your info, she’s never had any problems, but different countries says conflicting thing sometimes. I just want what is best for my fur child

  57. I don’t understand why pet food companies sell brewers yeast with garlic as a flea preventative if garlic is known to be toxic to dogs. Don’t these companies have our pets best interest and/or good health in mind? We assume that if a reputable company is selling a product for our pets that it must be okay for them. It’s incredibly disappointing that this is not the case.

  58. Alexandra says on  06/18/2012 at 6:31 pm

    I am very strict on telling our 6year old not to feed any table food to our 7month old Puggle… But he got a hold of some fat free popcorn and LOVES it…. :-)

  59. Wilda says on  06/18/2012 at 6:33 pm

    My vet PRESCRIBED garlic pills to my small dog to get rid of internal parasites. His breath was hard to tolerate while he took it, otherwise he was a-ok. I’d take that over chemical pesticide and neurotoxins any day.

  60. Sharon Barker – your vet is right! Garlic is good for dogs – like so many herbs that are ignored by conventional vets. Huge amounts of garlic can cause anaemia, but please give your dogs 1 or 2 crushed cloves per day in the raw meat meal. One of its many benefits is that it wards off worms and fleas. Have used it for years since starting to breed dogs. Never needed conventional dewormers which are far more toxic. Onion is a no no

  61. this dog is more adorable then boo the cutest dog in the world

  62. Alexandra says on  06/18/2012 at 8:01 pm

    There is a garlic powder for dogs expecially for dogs from the vet. It contains the garlic and minerals.

  63. Jessica says on  06/18/2012 at 8:09 pm

    i use garlic powder(springtime brand) for both my dogs to keep the bugs away. works amazingly well and have not had any problems with it!

  64. Shawn Finch, DVM says on  06/18/2012 at 9:41 pm

    Thank you for all your thoughtful comments! I sure did not mean to upset the Honest Kitchen and garlic-for-flea-protection folks. I totally understand why those can be reasons to use small amounts of garlic.

    I still contend that any amount of preventable red blood cell destruction is not ideal, and I do avoid allium with our pets, but everything we do for our pets is a risk trade off, and I understand how giving very small amounts of garlic for the benefit it can provide may be worth it for some dog lovers. And please do not leave your vet for suggesting garlic for fleas – talk with him or her and decide what you think is best for your pet.

  65. debrae says on  12/08/2012 at 11:14 pm

    my puppy just got into my dinner and ate some onions…
    what do i do now?

    • Anonymous says on  12/15/2012 at 12:02 pm

      Debrae, call your vet or animal emergency clinic for advice when this happens. and watch your dog for signs of illness.

  66. Dianna says on  05/15/2013 at 6:19 pm

    Last Thursday I fed my dog some left over thawed stir fry vegetables. Not realizing onions were a problem, there were a good number of onion pieces in the veggies. Sunday, the dog vomited and was eating grass. Monday he was very lethargic and seemed to be in pain. Tuesday afternoon / night he seems to be over whatever was wrong. He is a lab. He weighs approximately 100 pounds. Do you think it could have been the onions and if so, what are the lasting effects of a dog eating onions. Like I said, he seems to be better now.

    • Emmsy says on  02/05/2014 at 1:23 pm

      He may just have less red blood cells because onions make them burst but he will be fine.

  67. zoobee says on  06/29/2013 at 7:41 pm

    Hi Shawn, Thank you for the informative article. I have a question I can’t seem to find an answer to anywhere online, I was wondering if you could answer it. I just made a large volume of chicken stock which included an onion and a half to at least 8 lbs of chicken bones and meat plus carrots and celery. The onions were boiled with the stock for over 2 hours and all the liquid was drained away. I then ground up all the remaining solid with the intention of supplementing my dog’s food with it. Halfway through, I vaguely recalled that onions were no good, and pulled out around 1/2-3/4 an onion’s worth of remaining pieces. The yield is somewhere around 4 quarts of chicken mush, resembling tuna salad, within which is no more than 1 onion total, stripped of all its juices, etc. Wouldn’t the organosulfoxides have boiled away after 2 hours, leaving just fiber? I would like to feed my 50 lb Cattle Dog about 3/4 cup of this mix a day. Is that safe?

  68. Anonymous says on  07/26/2013 at 3:39 am

    I gave my chiuaha some left over French onion dip which was about 2-3 tablespoons ROUGHLY as a treat. I’m worried now :( he weighs about 6lbs.

  69. Emmsy says on  02/05/2014 at 1:19 pm

    If I put onions in gravy just for the taste but not actually give my puppy any onions is that ok? Also I believe that homecooked food is alot better for dogs than a raw diet or dog food. First of all becuase u know what is going into it and it contains alot more nutrition and healthy food.

  70. Anonymous says on  11/08/2014 at 9:27 pm

    You know, I’m reading conflicting information all the time, so I decided to trace the origin of this thinking through the research. Believe it or not, this is the TENTH article I have read and not one author has cited references.
    I like to follow up referenced research, and then I follow up on who they cite, and so on. It seems to be the only way of validating all the ” rules”

  71. Anonymous says on  02/02/2015 at 3:06 pm

    What about everyone who gives their dogs garlic to rid them from fleas?

  72. Anonymous says on  03/15/2015 at 4:06 pm

    I Agree If Cooked Onions Are So toxic Why Are My Grandparents Dogs Living So Long They Always Feed Them Left Overs With Cooked Onions

  73. Anonymous says on  03/30/2015 at 11:44 am

    How long does the symptoms last and Hw do u gt them better? X

  74. Chad says on  04/05/2015 at 11:23 pm

    All of this is great advice because I am sure we all know of our or many of our friend’s dogs who have died from grapes, onions, garlic etc…Yup, I gave some onion to my roommate’s dog and she mentioned that it is poisonous. So I looked it up and found this site. What’s completely absurd to me(almost as much as reading these posts) is that her dog’s breed has been around for around 500 years and never in the history has anyone said any food item you people have mentioned is deadly?! AND, ON TOP OF THAT, I have never seen, nor has anyone I have ever met, had a dog die from any of these! Even chocolate! I feel like everyone is going crazy. Even the dog^ that was said to die from chocolate…we don’t know the facts about that case. And, if chocolate truly is deadly, put that one on the “deadly” list. OK, got it…What about the rest? Every time a child feeds the dog under the table does the mother lose her mind? No! And they all lived to their proper age!! So, if everything was so deadly we would all know what to feed or not feed dogs. We would constantly be reminded as children. But, we were not and I would bet that every person’s dog on this forum probably always lived to their proper age. What is a little disturbing to me is the self-righteousness of all of your point of views. So, what makes you all think you finally figured all this out? Like I said, this dog breed sitting next to me is around 500 years old. So the internet got big in 1997…ish. So, finally the word of perilous food for dogs can be spread to benefit the world. Or, finally, people actually care about their dogs!!?? You people scare me. I’m serious. I always wondered how the Nazis were ever able to come to power. You gave me a glimpse. Thanks a lot.

  75. Anonymous says on  07/12/2015 at 11:55 pm

    I found this site because my dog ate a tiny piece of onion that fell to the floor while I was cooking, and I knew that onion is harmful. I don’t think that it is unreasonable to try to try to keep one’s pet safe, but I don’t want to buy into hysteria either. From what I’ve read, onions do pose a real threat in sufficient quantities. The science is there. A one time exposure in a minimal quantity is probably not going to be significant. As an aside, years ago I had two cats that ate an entire box of liqueur filled chocolates. They bounced off the walls (literally) for several hours, but suffered no apparent ill effects.

  76. diamond girl says on  08/13/2015 at 8:41 am

    I have just finished reading a book on holistic medicine for your pet and one on making your own dog’s food. Now I am reading more on line about feeding.. Garlic is used for intestinal parasites and is a natural way to ward off fleas. Both sources say its appropriate for dogs. The vet who wrote “The Nature of Animal Healing” has had years of experience healing animals, after other vets want to just “put them to sleep.” Of course any animal can have sensitivities/allergies to anything. Onions are avoided for the reasons stated in this article (thiosulphate).Garlic has much less. 1/5th to 1/10th and the amount used is smaller. The only real clinical study ever done used large amounts of garlic and saw some drop in RBCs but no clinical signs with the dogs. That said dogs can eat much of what we do and are better for it. The petfood you buy for you dog at the store is not regulated or inspected, It’s really anything goes from the sweepings off the floor at the slaughterhouse to the rendering plants where euthanized dogs and cats are turned into food for your pet, collars and all. Remember that means the poison that killed the animal in the first place is being eaten at every feeding!!.
    This is in all 50 states folks! What are animal by products anyway? Wonder why your pet gets cancer? Seizure disorders? Diabetes? etc.
    They are full of GMO grains with their added herbicides and pesticides, artificial coloring and flavorings to get the animals to eat it. And since they cook the stuff to death they add back artificial vitamins. YUCK Do you eat the same thing every day for every meal? I believe most pets die of malnutrition or poisons that we or our vets give them.
    My dogs have been eating from our table their whole lives and are very healthy. I learned the hard way when my first baby died of seizures immediately after getting her vaccinations…… that seizures are one side effect. Cancers at the injection site are another. Vaccines are full of heavy metals/toxins too, more and more are given today because they are an income stream for your vet. Why else take a healthy animal into the vet? Vaccines induce an immune response for at least 7 years. but they vaccinate every year? Why$$$$ The holistic vet recommended getting titers to check immunity first. It they are protected re-vaccination is not needed.
    Thanks for sharing your experience and ideas here.. These are only my opinions from what I have learned so far. I’m still searching and learning..

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