Foods toxic to dogs and cats: what is dangerous and how much is too much

Most pet poisonings do not happen in the garage among the chemicals. They happen in the kitchen – a square of chocolate from a holiday platter, raisins that fell out of a cake, a packet of chewing gum in a bag left on the floor. Foods that are entirely harmless to us can be a genuine medical emergency for a dog or a cat, not because they are spoiled, but because their metabolism simply cannot break them down the way ours does.

This guide collects what veterinarians actually see in practice: which foods are dangerous, at what quantities trouble starts, and what to do in the first half hour. The figures come from veterinary references (MSD/Merck Veterinary Manual, Cornell University, the ASPCA Animal Poison Control Center) and are meant to help you judge risk – never to replace a veterinarian's assessment.

Why food that is harmless to us can poison a dog

The difference is almost always the speed of breakdown. Theobromine from chocolate has a half-life of roughly 17.5 hours in dogs, compared with only a few hours in people – so a dog does not clear it as it goes, it accumulates until it reaches a level that irritates the heart and nervous system. Xylitol works the same way: in dogs it triggers a very rapid insulin surge, three to seven times the normal amount, sending blood sugar into free fall. In humans, the same sweetener behaves perfectly harmlessly.

Cats are a slightly different story. Their red blood cells are particularly prone to oxidative damage, so the compounds in onion and garlic affect them at far smaller quantities than dogs. According to the MSD Veterinary Manual, cats are the most susceptible species to Allium toxicosis.

In food poisoning cases what matters is not what the animal ate, but how much per kilogram of body weight. The same square of dark chocolate is a completely different problem for a 3 kg Chihuahua than for a 40 kg St. Bernard.

And one factor owners routinely underestimate: the urge to scavenge is partly genetic. A study published in Cell Metabolism in 2016 identified a deletion in the POMC gene in Labrador Retrievers and related retrievers, associated with greater food motivation and a tendency to obesity. If you live with a breed that “clears the table”, kitchen safeguards are not overkill.

1. Chocolate and cocoa

Chocolate is one of the most common reasons for an emergency call every year, peaking at Christmas and Easter. The culprits are theobromine and caffeine (together, methylxanthines), most concentrated in the bitterest products. White chocolate contains a negligible amount; cocoa powder contains almost seven hundred times more.

According to the MSD Veterinary Manual, dogs show first signs (vomiting, diarrhoea, excessive thirst) at around 20 mg of methylxanthines per kilogram, cardiac arrhythmias at 40–50 mg/kg, and seizures at 60 mg/kg or more. The table below translates that into grams of chocolate.

Approximate amount at which first signs may appear in a dog (20 mg/kg):

Signs usually appear within 6 to 12 hours and in severe cases can persist for up to 72 hours. Seizures require roughly three times the amounts in the table – but because individual sensitivity varies and theobromine content differs between products, the table is there to help you judge how urgent the call is, not to justify waiting it out.

2. Grapes, raisins and currants

This is the most treacherous item on the list. For nearly twenty years vets knew that grapes caused acute kidney injury in dogs, but not why. The puzzle was solved by a case of a dog that fell ill after eating homemade play dough – the ingredient that connected all the cases was cream of tartar.

“Tartaric acid, a nephrotoxin in dogs, is the common denominator and the likely toxic component.” – ASPCA Animal Poison Control Center

The practical consequence: it is not only grapes and raisins that are dangerous, but also currants, sultanas, tamarind and cream of tartar in home baking or play dough. According to Cornell University, grape juice, jelly, grape seed oil and wine have not been associated with the syndrome.

There is no safe threshold. MSD notes that more than one grape or raisin per 4.5 kg of body weight may contain enough tartaric acid to pose a kidney risk, while Cornell stresses that the exact toxic dose is unknown and some dogs become far sicker than others. Vomiting or diarrhoea appear within 6–24 hours, and kidney failure develops within 24–72 hours – and once a dog stops producing urine, the outcome is often poor.

3. Xylitol: a sweetener that endangers dogs but not cats

Xylitol (labelled E967 or “birch sugar”) is the sweetener in sugar-free products: chewing gum, mints, toothpaste, supplements, some medicines and protein bars. In dogs it triggers a rapid insulin surge and therefore hypoglycaemia, and at higher doses, liver damage.

MSD gives two thresholds: above roughly 100 mg/kg a drop in blood glucose is expected, and above 500 mg/kg there is a risk of severe hepatic failure. For a 10 kg dog the first threshold is about one gram of xylitol – with some gums, the content of just a few pieces. Signs can appear within half an hour, though with gum the slower release can delay them by 12 to 18 hours.

An important distinction many articles miss: xylitol is described as a canine problem. According to the MSD Veterinary Manual, dogs are the only domestic species in which xylitol toxicosis has been reported, and cats are not at risk of either hypoglycaemia or liver injury. That is no reason to offer it to cats – but it is a reason to know where you stand if an accident happens.

4. Onion, garlic, leek and chives

Plants of the genus Allium contain sulphur compounds that damage red blood cells and cause so-called Heinz body haemolytic anaemia. They are toxic in every form – raw, cooked, dried and powdered – which means soups, sauces, spice blends and leftover pizza count too.

The quantities differ sharply between species. According to the MSD Veterinary Manual, in cats less than a teaspoon of cooked onion or 5 g of raw onion per kilogram is enough, while in dogs signs have been described at 15–30 g of raw onion per kilogram. Garlic is 3 to 5 times more toxic than onion.

The delay is what makes this poisoning dangerous. Heinz bodies begin forming within 24 hours and peak at around 72 hours, but clinical signs of anaemia only appear several days later: weakness, pale gums, yellowish skin and eyes, dark urine, rapid breathing. An animal that seems “completely fine” after eating onion is therefore no proof that all is well.

5. Alcohol and raw yeast dough

Raw yeast dough is a double hazard. The stomach is an ideal incubator for yeast: the dough keeps rising inside it and stretches the stomach wall much as in bloat, while fermentation simultaneously produces ethanol that is absorbed into the bloodstream. According to the MSD Veterinary Manual, death is usually caused by the metabolic effects of the alcohol rather than by the distension itself.

Signs: unproductive retching, a distended abdomen, lethargy, then disorientation, loss of coordination, hypothermia, low blood sugar and, in severe cases, seizures. The alcohol side of the story applies equally to drinks, rum cake, punch and fruit steeped in spirits.

6. Macadamia nuts and other nuts

Macadamia is a curiosity: the mechanism of toxicity is still unknown, and it has only been reported in dogs. According to MSD, signs appeared at 2.4 g of nuts per kilogram of body weight – weakness, hind limb unsteadiness, tremors, ataxia, vomiting and raised body temperature, typically within 12 hours. The good news: most dogs recover within 12 to 48 hours, often without specific treatment.

Other nuts are not specifically toxic, but they are very fatty; the ASPCA warns that large amounts of fat can cause vomiting, diarrhoea and even pancreatitis. The greatest risk is the combination: macadamias in dark chocolate merges two hazards in a single bite.

Quick reference

What about avocado, milk and bones?

A few foods from the usual “black lists” deserve a more precise verdict.

Avocado. It contains persin, but according to the MSD Veterinary Manual dogs and cats are relatively resistant – the genuinely vulnerable animals are birds, rabbits, rodents and livestock. In dogs the main risk is mechanical: the pit can cause a gastrointestinal obstruction, and the flesh is fatty.

Milk and dairy. Not toxic. Most adult dogs and cats lack sufficient lactase, so as the ASPCA notes, milk causes diarrhoea and digestive upset – unpleasant, but not an emergency.

Bones. The problem is injury, not poisoning: the ASPCA warns that bones can cause injury or obstruction of the gastrointestinal tract. Cooked bones splinter into sharp fragments and carry the highest risk.

Dangerous foods for parrots, rabbits and rodents

For other pets the list changes significantly. Avocado is far more dangerous to birds than to dogs – MSD explicitly lists budgerigars, canaries and cockatiels among susceptible species, where it can end in laboured breathing, swelling and death. Chocolate and caffeine are toxic to birds as well.

With rabbits and rodents the biggest trap is different: their digestion is built for hay and fibre, so even “innocent” human treats harm them – sweets, bread, nuts and excessive fruit. We cover this in detail in our guides to a rabbit's diet: what they can and cannot eat and what hamsters eat. What each species needs can be found in our directories of parrots, rabbits and rodents.

First aid: the first 30 minutes

If you suspect your animal has eaten something on this list, the order of actions matters more than raw speed.

1. Move the animal away from the source and collect the remains and packaging.
2. Establish four facts: what, roughly how much, when, and how much the animal weighs. These are exactly what the vet will ask for first.
3. Call your vet or the nearest emergency veterinary clinic. Do not wait for symptoms – with grapes and onion they appear far too late to be a useful warning.
4. Take the packaging with you. The label reveals the theobromine or xylitol content, and therefore the actual dose.
5. Do not induce vomiting without explicit instruction from a vet.
6. Do not give “home antidotes” – no milk, oil, salt or human medicines.

Frequently asked questions

How much chocolate is dangerous for a dog?

It depends on the dog's weight and the type of chocolate. First signs in dogs are described at around 20 mg of methylxanthines per kilogram, which for a 10 kg dog means roughly 87 g of milk chocolate but only about 37 g of dark. For cocoa powder the threshold is around 7 g.

Can a single raisin be dangerous?

It can. MSD notes that more than one raisin per 4.5 kg of body weight may pose a kidney risk, and no safe threshold has been established. For a small dog, even a handful of raisins is reason to call the vet.

Are grapes dangerous for cats too?

The kidney failure syndrome is documented in dogs; in cats the link is not confirmed. Because the data are insufficient, grapes and raisins should still not be offered to cats.

Is xylitol dangerous for cats?

On current evidence, no – MSD lists dogs as the only domestic species with documented xylitol toxicosis.

My dog ate onion but seems completely healthy. Is the danger over?

No. Heinz bodies form within the first 24 hours and peak at around 72 hours, and signs of anaemia only appear several days after ingestion. A symptom-free first day is not a guarantee.

Can a dog have a piece of bread or cheese?

Neither is on the toxic list. Just watch the ingredients (raisins, onion, xylitol in sugar-free products) and the fat content in sensitive dogs.

Is white chocolate safe?

It contains a negligible amount of methylxanthines (0.04 mg/g), so there is practically no risk of classic poisoning. It is still very fatty and sugary, which does not suit dogs.

What about coffee and energy drinks?

Caffeine acts just like theobromine, only faster. Coffee grounds, coffee capsules and energy drinks are a serious risk to dogs and cats and belong in a closed bin.

In closing

The great majority of these cases end well – provided the owner calls early enough. The best protection is not memorising every number, but two things: keeping dangerous foods physically out of reach, and having your vet's number to hand before you need it. If you are unsure whether the amount eaten matters, call – an assessment over the phone is always cheaper than a night at the clinic.

For more on the daily care and feeding of individual species, see our directories of dog breeds and cat breeds, and for the first weeks with a new pet, our guide to a kitten's first days in a new home.