The Canine Ledger

Foods That Are Toxic to Dogs, With the Actual Evidence

Chocolate, grapes and raisins, onions and garlic, and xylitol: what each one does, how fast, and why we don't print a safe amount for any of them.

Written by thecanineledger

This page carries no advertising, and nothing on it is for sale.

If your dog has just eaten any of the foods on this page, phone your vet, an emergency clinic or an animal poison helpline now. Don’t wait for signs. Several of these do their damage before the dog looks ill.

Food and drink are the second most common reason people phone ASPCA Poison Control in the United States. In 2025 they made up 16.4% of calls, and the ASPCA names the foods behind most of them: “Grapes, raisins, xylitol gums, onions and garlic make up the largest part of this group.” Chocolate, counted separately, made up another 13.6% (ASPCA, Top 10 Toxins of 2025).

Those four, chocolate, grapes and raisins, onions and garlic, and xylitol, are what this page covers. Each has a chapter in the Merck Veterinary Manual written by an ASPCA toxicologist, and each is quoted below.

One thing you won’t find here is a “safe amount.” That is deliberate, and §6 explains why.

1. Chocolate

What does the harm: two stimulants, theobromine and caffeine. How much a bar contains depends on the type of chocolate and on the brand. The Merck Veterinary Manual notes that “The exact amount of methylxanthines in chocolate varies because of both the natural variation in cocoa beans and the variation among different chocolate product brands” (Merck, Chocolate Toxicosis in Animals).

What it does: affects the heart and the nervous system. Merck lists the early signs as thirst, vomiting, diarrhoea, a swollen belly and restlessness, which “may progress to hyperactivity, polyuria, ataxia, rigidity, tremors, and seizures.”

How fast: “Clinical signs of chocolate toxicosis usually occur within 6–12 hours after ingestion.” That delay is why a dog who seems fine an hour later is not in the clear.

The part people forget: chocolate is fatty. Merck notes that “The high fat content of chocolate products also may trigger pancreatitis in susceptible animals.” A dog who eats a box of chocolates can be ill from the fat as well as the stimulants.

What a vet does: if the dog is still well and it was recent, usually makes them vomit, then manages any heart or nervous-system signs. Merck notes that “No readily accessible diagnostic tests for chocolate intoxication exist”, so the vet works from what you tell them. Bring the wrapper.

2. Grapes, raisins and currants

What does the harm: probably tartaric acid, though this isn’t settled. Merck says “One proposed toxic principle in these fruits is tartaric acid”, which dogs are poor at getting rid of (Merck, Grape, Raisin, and Tamarind Toxicosis in Dogs). Tamarinds carry the same risk.

Which currants: the dried “currants” in baking (Zante currants) are a kind of grape and count. Merck notes that “Ingestion of true currants of the genus Ribes has not been associated with renal injury”, which means fresh blackcurrants and redcurrants are a different plant. If you aren’t sure which you have, treat it as a grape.

What it does: damages the kidneys. Merck: “Most dogs with grape, raisin, or tamarind toxicosis develop vomiting or diarrhea within 6–12 hours after ingestion.” Kidney failure, in which the dog stops producing urine, “develops within 24–72 hours after exposure; once anuric renal failure develops, most dogs die or are euthanized.”

Why it is unpredictable: “The tartaric acid content of grapes, raisins, and tamarinds varies, resulting in variable effects following ingestion.” Some dogs eat raisins and are fine. Others don’t survive. Nobody can tell you in advance which your dog will be.

What a vet does: if the dog is still well, makes them vomit promptly. After a large amount, or if diarrhoea starts, Merck recommends a drip for at least two days while kidney function is watched.

→ Grapes and Raisins: What We Know, and the Tartaric Acid Question

Our note: We don’t print Merck’s grape and raisin threshold, because no amount is known to be safe.

3. Onions, garlic, leeks and chives

What does the harm: sulphur compounds released when these plants are chopped, cooked or chewed. They damage red blood cells.

Which forms are worst: concentrated ones. Merck says toxicosis in dogs is “most commonly associated with ingesting concentrated forms of Allium, such as dehydrated flakes, powders, or dry onion soup mixes”, and that “Garlic is 3–5 times more toxic than onion” (Merck, Garlic and Onion Toxicosis in Animals). Raw and cooked onions can both cause it. This matters for leftovers, gravy and stock, which can contain onion or garlic powder.

What it does, and when: this is the slow one. Damage to red blood cells starts within a day, but “Clinical signs of Allium spp toxicosis are generally not noted until substantial hemolysis has occurred, usually a few days after exposure.” The signs are those of anaemia: tiredness, weakness, pale gums, fast breathing, sometimes red or brown urine and yellowing.

Why the delay matters: a dog who ate a dish of onions on Saturday may not look unwell until Tuesday. Tell your vet what they ate and when, even if it was days ago.

Our note: “Red or brown urine” and “pale gums” are our plain-language descriptions of Merck’s findings.

4. Xylitol

What it is: a sugar substitute. Merck describes it as “a sugar alcohol used to sweeten sugar-free products, such as gums, candies, mints, peanut butter, and baked goods”, and notes it also turns up in non-food products, including medicines (Merck, Xylitol Toxicosis in Dogs). Some chewable vitamins contain it. → Why Adding a Multivitamin Doesn’t Fix an Unbalanced Recipe

What it does: in dogs, it causes a sudden, severe drop in blood sugar. Some dogs also get liver damage, and Merck notes that the mechanism “is unknown.”

How fast: this is the fast one. “Clinical signs of hypoglycemia can develop within 30 minutes after ingesting xylitol or may be delayed up to 12–18 hours if the xylitol is in a substrate that slows absorption (eg, some gum products).” Signs of low blood sugar include vomiting, weakness, wobbliness, seizures and collapse. Liver damage may not show for a day or two.

Check the label. If a sugar-free product is involved and you can’t tell whether it contains xylitol, phone and ask.

→ Xylitol: Where It Hides, and Why Minutes Matter

Our note: We haven’t found a veterinary or regulatory source on other label names for xylitol.

5. If your dog has eaten one of these

Phone now, before signs appear. For grapes and xylitol in particular, treatment works best before the dog is ill. Have ready:

  • what it was, with the packaging if there is one;
  • roughly how much is missing;
  • when it happened;
  • your dog’s weight.

Don’t make your dog vomit unless a vet tells you to, and never with salt. → My Dog Ate Something: Why You Shouldn’t Make Them Vomit Without a Vet

If your dog is already showing signs, such as repeated vomiting, trembling, wobbliness, collapse or a seizure, go to the nearest emergency clinic and phone on the way. → Emergency Signs in Dogs: When to Go Now, Not Tomorrow

→ Animal Poison Helplines by Country: Numbers, Fees, and What Works From Where

6. Why we don’t print a “safe amount”

You will find calculators online that tell you how much chocolate is dangerous for a dog of a given weight. The Merck Veterinary Manual itself gives figures for chocolate and grapes. We have chosen not to print any of them, for three reasons.

The amount in the food varies. Merck says so for both chocolate and grapes, in the passages quoted above.

Dogs vary. For chocolate, Merck notes that “individual susceptibility to methylxanthines varies.” For grapes, some dogs are harmed by small amounts and others are not, and nobody knows why.

A number gets used the wrong way. An owner who reads a threshold at 1am and works out that their dog ate “less than that” may decide not to call. That is the one outcome this page exists to prevent. A vet or a poison helpline can do the same calculation, with the actual product in front of them, and tell you what it means for your dog.

Our note: A dog that licked one milk-chocolate button may end up at an emergency visit it didn’t need. We’d rather that than the opposite.

7. What else is on the lists

Many websites list other foods as dangerous to dogs: macadamia nuts, alcohol, coffee and caffeine, raw bread dough, avocado, and more. We haven’t read the primary sources for those yet, so they aren’t on this page. They will be added, with their evidence, when we have. If your dog has eaten any of them, the advice in §5 still applies: phone.

8. What we could not verify

Commonly saidWhat we found
“A little chocolate won’t hurt”It depends on the chocolate and the dog, which is why we don’t give an amount. Merck notes both the chocolate and individual susceptibility vary.
“White chocolate is safe”Not checked yet. We haven’t found the figures in a source we have read. Phone if in doubt.
“Only a large number of grapes is dangerous”Not reliable. Merck: effects vary because the toxic content varies.
“Grapes are toxic because of pesticides or mould”Not what the current evidence points to. Merck names tartaric acid as one proposed cause. It is not proven.
“Cooked onion is safe”Wrong. Merck: raw, cooked, dehydrated and granulated onions and garlic have all caused toxicosis in dogs.
“A bit of garlic is good for dogs”Not supported. Merck rates garlic as 3–5 times more toxic than onion. We found no evidence of a benefit in the sources we read.
“Blackcurrants are as dangerous as raisins”Not according to Merck, which says true currants (Ribes) have not been linked to kidney injury. Dried “currants” in baking are a grape.
Dose calculators for chocolate or grapesNot printed here, for the reasons in §6.

Sources

Always confirm with your vet before acting on anything on this page.