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Bad Food For Dogs

chocolate bar with white background

Pete The Vet General

Every species of animal has a unique metabolism, and as a result, every animal has a different sensitivity to different poisons. Furthermore, some substances that are edible for some species can be toxic to other species.

This issue causes particular problems for dogs that live with humans: we presume that if we can eat some things, so can dogs. That is not necessarily the case, as you’ll see from this list of human foodstuffs which can be toxic to dogs.


 Chocolate contains the stimulant theobromine. This gives humans a pleasantly buzzy lift in mood, but it can poison dogs. The lethal dose is around 1 to 2.5 grams of threobromine for a 10kg dog. This can be as little as two ounces of dark baking chocolate. Milk chocolate is less poisonous, and white chocolate is harmless. It’s best to keep all chocolate away from dogs, because even if they are just given small treats, they will develop a taste and desire for it, which may make them more likely to steal it if they get a chance. You can find an online chocolate toxicity calculator here.

Coffee and tea 

These contain caffeine, which again, makes humans feel mildly stimulated, while it can cause toxic effects in pets. For 10kg dog, the lethal dose is around 1.5g.  A cup of regular coffee could contain as much as 150mg of caffeine, so this dog would need to drink 10 cups which is obviously unlikely to happen.  Dark tea may contain up to 100mg caffeine, so again, the risk is low. Nonetheless, owners should be sensible if offering caffeinated drinks as “treats”.

Onions and garlic

Onions and garlic contain organothiosulphates, a type of chemical which damage red blood cells. While the quantities of these vegetables that are used to flavour human meals are generally safe, but there are incidents where dogs have become anaemic after grazing on fields of spring onions.

Grapes and raisins

Grapes and raisins seem harmless, but in 2001 the first article was published about their toxicity to dogs, and since then, cases have been recorded across the world. In the UK, there were 23 cases between 2003 and 2005.  The toxic agent remains unknown and it is not always present in grapes. It has been suggested that it may be associated with some sort of invisible fungal contamination which is why it’s an intermittently present toxin. When grapes contain the toxin, the result can be severe, terminal renal failure after just small quantities of grapes or raisins.  The lowest dose that has been known to cause poisoning is 20g/kg of grapes (perhaps 20 grapes for my 10kg dog), or 3g/kg of raisins (about 20 – 30 raisins for my 10kg dog).  In one study, 60% of dogs that ate large amounts of grapes were poisoned: vets now suggest that every dog that has eaten grapes or raisins should be treated intensively to reduce the risk of complications.


Avocado is eaten by people all over the world, but all parts of the avocado tree and fruit contain a chemical called persin that can cause damage to specific cells in the heart and the mammary glands in birds and animals. It’s not a big risk to feed occasional teaspoonful’s to dogs, but still, it’s best avoided. There was one case report in 1994 of two dogs that loved eating avocados that died of heart failure.

Macadamia nuts

Like grapes, contain a toxic compound that has not yet been identified;. This toxin has been associated with lethargy, weakness and collapse in dogs when eaten in moderate amounts (between 2.2 and 64g/kg: if one nut weighs 3g, a 10kg terrier would have to consume between 7 and 20 nuts). It isn’t a fatal poison: all affected dogs in case reports have made a full recovery, but it’s still safest not to feed these to your pet.

Brewing hops

Brewing hops contains a number of compounds that can be poisonous, and if you enjoy home brewing, there is a risk that your pet dog may try to eat some of the residue if you leave it in a place where they can reach it.  The toxin causes “malignant hyperthermia”, causing the body temperature to shoot up to a dangerous level. Emergency treatment is needed to save the lives of affected animals.


Salt is safe as a seasoning agent, but when dogs eat large quantities, the result can be fatal. Case reports include a Boxer which drank large volumes of salty water while swimming in the sea, some of dogs that ate playdough that had been left within their reach, and a Doberman whose owner forced her to consume ten teaspoonful’s of salt in a misguided effort to make her sick after she’d eaten chocolate.


Xylitol is a natural sweetening agent found in many fruits, and it’s also manufactured synthetically to be used as a sweetener human food products (where it’s known as “E976″). It’s found in chewing gum, sweets and toothpaste: it has useful plaque-reducing properties, as well as causing a pleasing cooling effect on the tongue. The first known case of toxicity in dogs happened in 2004, after a young adult Labrador consumed around 100 pieces of sugar-free chewing gum. The dog collapsed, suffering from a low blood sugar, but made a rapid recovery after treatment.  Many other cases have since been reported, and some have died. Occasional treats containing xylitol will not do any harm, but as with chocolate, such products should be kept out of reach of dogs to stop them from feasting on them.


Alcohol can be poisonous for dogs, just as for humans. A couple of measures of whisky could cause severe poisoning to a 10kg dog. There’s a reported case of a dog in Austria which developed alcohol poisoning after eating 500g of raw yeast dough. The fermentation of yeast in his digestive tract generated enough ethanol to bring about a blood alcohol level in the dog higher than the legal limit for driving.  Additionally, raw dough should be kept away from dogs for a different reason, in that it if it expands inside the digestive tract, it can cause a painful and dangerous blockage.)


There are many other foods that can cause problems for dogs, if not outright toxicity. Adult dogs lack the enzyme to digest lactose, so large quantities of any dairy products can cause diarrhoea. Raw egg whites can also have this effect, so should only be given in small quantities.  The wood-type stones of many fruits (apples, pears, plums, apricots, peaches, nectarines and cherries) contain a chemical that can be poisonous if they’re cracked open and swallowed. Some raw vegetables (including cassava, common beans and runner beans) also contain agents than can irritate the digestive tract so are best avoided.

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