Toxic foods and household hazards

Organosulfur compounds (thiosulfates and related species) oxidise feline haemoglobin, forming Heinz bodies and destroying red blood cells. The result is haemolytic anaemia, which may appear days after ingestion rather than immediately.

Dose

Cats are considerably more sensitive than dogs. Around 5 g of onion per kilogram of body weight can cause clinically significant changes; that is roughly a tablespoon for an average cat. Concentrated forms are the real hazard: garlic and onion powder are many times more potent by weight than the fresh vegetable, so baby food, gravy, stock, soup, and seasoned meat matter more than a scrap of raw onion.

Signs

Lethargy, weakness, pale or yellow gums, rapid breathing, dark or reddish urine, collapse. Often delayed by one to five days.

Note

Garlic is not a safe flea remedy. That advice circulates persistently and is wrong.

Methylxanthines (theobromine and caffeine) that cats metabolise slowly. Toxicity rises with cocoa concentration: baking chocolate and cocoa powder are far more dangerous than milk chocolate, and white chocolate is essentially fat and sugar. Causes vomiting, hyperexcitability, tremors, tachycardia and arrhythmias, hyperthermia, and seizures. Cats seek chocolate less than dogs because they cannot taste sweetness, but they do get into cocoa powder, coffee grounds, and discarded tea bags.

Ethanol depresses the central nervous system profoundly in a small animal; even small amounts cause vomiting, disorientation, hypothermia, respiratory depression, and coma. Raw bread dough is a double hazard: it expands in the warm stomach causing painful distension, and fermentation produces ethanol internally. Also relevant: rum-soaked fruit, liqueur chocolates, and unbaked dough left to prove on a counter.

Well documented to cause acute kidney injury in dogs, with the mechanism now believed to involve tartaric acid. The evidence in cats is thin (mostly because cats rarely eat grapes) so the risk is uncertain rather than established. Given the severity of the outcome in dogs, the standard veterinary advice is to treat any ingestion in a cat as potentially serious and call for advice.

Three separate problems. Raw fish and shellfish contain thiaminase, which destroys thiamine and, fed regularly, causes thiamine deficiency, anorexia, ventroflexion of the neck, ataxia, seizures, and death. Raw egg white contains avidin, which binds biotin. Both raw fish and raw egg also carry Salmonella risk. Cooked fish in modest amounts is fine; an all-fish diet is not, for this reason and because of vitamin E depletion and iodine load.

Not poisonous, but most adult cats are lactose intolerant, intestinal lactase declines sharply after weaning. A saucer of milk produces osmotic diarrhoea and adds a substantial number of empty calories to an animal prone to obesity. Lactose-free “cat milk” avoids the diarrhoea but not the calories.

In dogs, xylitol causes catastrophic insulin release, hypoglycaemia, and liver failure. In cats the picture is different: in the studies that exist, cats fed xylitol did not develop the hypoglycaemia and liver injury seen in dogs. That said, the data are limited, the substance has no business in a cat, and xylitol-containing gum, sweets, peanut butter, and toothpaste should be kept away from all pets.

Cooked bone splinters and can perforate the gut or lodge in the oesophagus. Large fat trimmings can trigger pancreatitis. Small cooked bones from a chicken carcass are a common emergency.

A stolen mouthful is harmless. As a diet it is dangerous: dog food is not formulated for feline taurine, arachidonic acid, retinol, or niacin requirements, and long-term feeding causes exactly the deficiency syndromes described in this guide.

Cats poison themselves on medication more than on anything else in the house.

Paracetamol / acetaminophen

The most dangerous common drug for a cat. A single regular-strength tablet can kill an average cat through methaemoglobinaemia and liver necrosis, because cats cannot glucuronidate it. Signs include brown or muddy gums, facial and paw swelling, laboured breathing, and dark urine. Never give a cat human painkillers under any circumstances.

NSAIDs: ibuprofen, naproxen, aspirin

Cause gastric ulceration and acute kidney injury at low doses. Aspirin has occasional veterinary use at very low, carefully spaced doses, which is a decision for a vet, not an owner.

Antidepressants, ADHD medication, sleep aids, decongestants

Pseudoephedrine, amphetamines, and SSRIs cause agitation, hyperthermia, tremors, and seizures. Cats are attracted to some tablet coatings.

Vitamin D supplements

High-dose human vitamin D causes hypercalcaemia and kidney injury.

Permethrin-based spot-on flea treatments made for dogs are severely toxic to cats, causing tremors, hyperthermia, and prolonged seizures that can be fatal. Cats lack the metabolic capacity to clear pyrethroids at canine concentrations. This happens most often when a well-meaning owner applies a dog product to a cat, but also when a treated dog and a cat sleep together in the days after application. Only use flea products labelled for cats, and separate treated dogs from cats until the application site is dry.

Sweet-tasting and readily lapped from a garage floor or a driveway puddle. As little as a teaspoon can kill a cat through calcium oxalate crystal deposition in the kidneys. The window for effective treatment is very short (hours, not days) so any suspicion of exposure is an immediate emergency. Propylene-glycol-based antifreeze is a much safer alternative product.

Cats cannot glucuronidate phenols and monoterpenes efficiently. Tea tree (melaleuca), pine, citrus, wintergreen, peppermint, eucalyptus, cinnamon, pennyroyal, and ylang-ylang are the frequently implicated ones. Both direct contact and prolonged exposure to an active diffuser in an unventilated room can cause drooling, ataxia, tremors, respiratory irritation, and liver injury. If you use a diffuser, do it in a ventilated room the cat can leave, and never apply oils to a cat's skin.