Healthy dogs are unlikely to die if they eat onions or garlic, but they may need a stay in an animal hospital to keep them comfortable.
Your vet might have to prescribe an IV medication to stop vomiting, and sometimes dogs that eat garlic will need blood transfusions.
Your dog might also need IV fluids to fight dehydration.
All Plants in the Garlic and Onions Family Are Toxic to Dogs
Farm-grown, garden-grown, and wild garlic and onions have been eaten raw and used in cooking for thousands of years.
There are at least 85 different species of edible plants in the Allium family.
This group of edible plants includes not just garlic and onions, but also chives, shallots, leeks, and scallions.
There are also 91 ornamental plants that are also toxic to dogs (and cats) in the Allium family.
Your dog can get allium poisoning by eating Stars of Persia or Giant Onions from your flower bed.
Most cases of allium poisoning in dogs, however, result from eating garlic, onions, leeks, or chives. All of these plants grow from bulbs.
The bulbs may be solitary or form clusters. They all have a distinctive garlic or onion odor when they are crushed.
The distinctive odor is an easy way to tell the difference between garlic and onions and outwardly similar plants—but just because a bulb doesn’t smell like garlic or onions doesn’t mean it is safe for your dog.
The bulbs of “death cannas” look like garlic but are even more deadly.
Chewing Releases Toxins in Garlic and Onions
Raw garlic, onions, and other plants in the Allium Family become toxic when they are chewed.
These pungent vegetables contain a chemical called alliin. If the vegetables aren’t chewed and digested, alliin stays inert and passes through the digestive tract with very little harm.
But if your dog chews a big piece of garlic or onion—and every dog loves to chew— the action of chewing and mixing the contents of plant cells with saliva converts alliin into allicin.
It’s allicin that becomes various kinds of canine-toxic compounds in your dog’s digestive tract.
Turning garlic into powder, or chopping or pressing it, also converts relatively harmless alliin to potently poisonous allicin.
If the allicin has been released from the plant cells that hold it, it remains toxic even if it is cooked, and even if the garlic has decayed or spoiled in the refrigerator.
Once allicin gets into a dog’s digestive tract, digestive juices turn it into a variety of burning compounds.
These compounds are “anti-antioxidants.” They are particularly harmful to red blood cells.
Dogs (and, to an even greater extent, cats) have limited amounts of antioxidants in their blood.
The chemicals from garlic and onions overwhelm the blood’s natural defenses, and red blood cells begin to break down.
But before red blood cells begin to break down they lose their ability to carry oxygen.
Instead of binding to hemoglobin that carries oxygen, red blood cells bind to a sulfur compound called sulfhemoglobin.
On a molecular level, it shoves oxygen out of the way and keeps it from binding to hemoglobin. It also causes tiny malformations in red blood cells called Heinz bodies that your vet can detect under a microscope.
Red blood cells lose their ability to generate clotting factors, so your dog becomes susceptible to easy bleeding.
Symptoms of Garlic or Onion Poisoning in Your Dog
The changes in red blood cells occur almost immediately after a dog consumes garlic, onions, or related plants.
The symptoms may not be obvious until a few days later.
Dogs that have garlic or onion poisoning may become lethargic. Allicin and a related garlic compound called ajoene slow down the heart.
Your dog may not have the energy to play. She may just want to curl up into a ball and take a nap.
Canine allium poisoning can make your dog unusually sensitive to cold. Allicin and ajoene also dilate blood vessels.
More blood stays near the surface of your dog’s body, where it can lose body heat.
If garlic or onion poisoning has gone on so long that the liver has been damaged, your dog may show signs of jaundice, yellowing around the eyes and gums.
Your dog’s abdomen may become tender and, in serious cases, also swollen. Your dog may not want to eat.
And let’s not overlook one obvious symptom: Dogs that suffer garlic or onion poisoning often have garlic or onion breath.
Raw garlic also releases compounds that irritate your dog’s stomach lining. (This problem does not occur with aged garlic.)
Your dog may develop vomiting and diarrhea, and become dehydrated as a result.
How Much Garlic or Onions Does It Take to Cause Serious Problems?
The answer to “How much garlic or onions will poison my dog?” is “A lot.” But damage from eating garlic and onions is cumulative.
If your pet gets garlic and onions every day, the effects add up.
The general rule is that 3 grams of garlic per kilogram of body weight can cause damage to red blood cells.
That’s the rough equivalent of a small clove of garlic for every 2 pounds your dog weighs.
If you have a three-pound Chihuahua, just one clove of garlic can make him very sick in just a couple of days.
If you have a 75-pound Labrador retriever, half a clove of garlic every day for a couple of months will result in serious anemia and probably lots of stomach upset, too.
Black garlic contains just 10% of the toxic allicin in minced white garlic. (That doesn’t mean it’s OK to give black garlic to your dog.)
Garlic added to soup has about half of the toxins in garlic that is roasted, and chopped garlic added to a salad dressing containing vinegar releases four times as much allicin as garlic used to flavor a roast.
Toxicity in onions varies the same way it does in garlic.
Raw onions added to acidic foods (such as lemon or vinegar) are a lot more toxic than onions added to a soup. Roasted onions are much less toxic than onion rings.
The more the garlic and onions are broken down, the more toxic they become for your dog.
But unless you have a very small dog, the real problem is giving your dog food that contains garlic or onions every day.
What Can Your Vet Do to Treat Canine Garlic Poisoning?
The first thing your vet will do when you bring your dog in with symptoms of garlic poisoning is to make sure garlic is really the problem.
Similar symptoms result when your dog eats cabbage or broccoli, mothballs, copper or zinc or vitamin K supplements, or gets into Tylenol, benzocaine pain relief ointments, vaping solutions, or antifreeze
Your vet will also want to make sure the symptoms don’t result from diabetes, fatty liver, overactive thyroid, or lymphoma.
Once it’s clear that garlic and/or onion poisoning is the problem, there is a limited number of treatment options.
If your dog ate a large amount of garlic recently, the vet might give activated charcoal to stop the harmful chemicals from being absorbed.
This treatment only works in the first one to two hours after the garlic and/or onions are consumed.
The vet may give a transfusion or put your dog on oxygen if hematocrit, hemoglobin, or red blood cell counts are low. IV vitamin C, vitamin E, and NAC (N-acetyl cysteine) can help your dog’s body recover needed antioxidants.
In most cases, with veterinary care, your dog will recover in a few days. Most dogs will need to be monitored in the animal hospital.
Dogs that don’t get veterinary treatment can’t get better as long as they continue to be fed garlic and onions, and dogs with other health conditions may not survive.
Prevention Is Better Than Treatment
The key to preventing garlic and onion poisoning is making sure that your dog doesn’t have access to either food.
Never give your dog food seasoned with garlic or onions, no matter how much they beg.
When you have leftovers that contain garlic or onions, put them in a container your dog cannot open.
Don’t leave foods containing these toxic ingredients out on a counter or table. Keep in mind that your dog may be able to get up on a counter or table.
And even if you have a cooking mishap that ruins the dish you are preparing, don’t assume your dog won’t eat just because it tastes bad.
It isn’t just garlic, onions, chives, leeks, and scallions that can make your dog sick. You also need to protect your pooch from eating:
- Bread dough. The yeast in bread dough makes it rise when it’s kept in a warm place. Your dog’s stomach is the perfect incubator for the yeast used to make bread rise. Dogs that eat bread dough can experience bloated stomachs, swollen abdomens, profuse flatulence, and depression from the alcohol made by the yeast. Because bread dough expands to many times its original size, just a small amount of bread dough can cause big problems for your dog.
- Broccoli. The toxic chemical in broccoli is isothiocyanate, which has some of the same effects as allicin from garlic and onions. It takes a lot more isothiocyanate from broccoli to poison a dog than allicin from garlic and onions. But dogs that get as much as 10% of the volume of their diet from broccoli, cabbage, and cauliflower may experience problems.
- Cannabis edibles. CBD can relieve pain in dogs. Cannabis edibles that contain the intoxicating compound THC, however, can produce unpredictable effects. It’s best to keep dogs and cannabis edibles separated.
- Chocolate. Coffee, tea, and chocolate all contain theobromine, the chemical that makes them so enjoyable for human consumption. This chemical has potent side effects even in people. It’s used as an asthma medication, for example. In dogs, a chocolate high can induce rapid heart beat, rapid breathing, vomiting, seizures, and, in puppies, even death.
- Cooked bones. Dogs thrive on raw bones. After all, their canine ancestors hunted and ate game. But cooked bones can splinter and puncture your dog’s throat or digestive tract. No dog should get any bones from cooked meat or fish. Bones from turkey, chicken, and ham are especially dangerous.
- Grapes and raisins. Veterinary researchers don’t know exactly which chemicals in grapes and raisins are so toxic to dogs, but eating grapes or raisins or slurping up wine can cause kidney failure in dogs.
- Macadamia nuts. These fatty, salty treats from Hawaii can cause weakness, depression, tremors, joint pain, and pale gums about 12 hours after dogs eat them. Cashew fruit can have a similar effect.
- Pits and seeds. Pits and seeds of stone fruits (apples, peaches, plums, and apricots, for example) contain cyanides. Dogs can experience the symptoms of cyanide poisoning after eating them, including rapid breathing, drooling, uncontrolled urination and defecation, muscle spasms, and coma. There is an antidote for cyanide poisoning, but the vet must administer it in time.
- Tomato stems, tomato leaves, and green tomatoes. Green parts of the tomato contain atropine, a chemical used to treat cardiac arrest. When dogs eat these parts of the tomato plant, they can experience dilated eyes, tremors, and rapid heartbeat.
- Xylitol. This sugar substitute used to sweeten chewing gum, toothpaste, breath mints, mouthwash, and candies can trigger a sudden release of insulin in dogs. They can go into shock and sometimes suffer serious liver damage.
Whenever you suspect your dog has eaten something toxic, seek help right away.
Call your vet as soon as possible, or if it’s not possible to take your dog to a veterinary emergency room. Here are the numbers to call:
- ASPCA Pet Poison Control Center at (888) 426-4435 in the US.
- Animal Poison Control Center at 800-213-6680 in Canada.
- Australian Animal Poisons Control Center at 1300 869 738 In Australia,
- New Zealand Animal Poison Control Center at 0800 869 738 in New Zealand.
- Royal Society for the Prevention of Cruelty to Animals at 0300 1234 999 in the UK.
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