The whole plant is toxic to cats — stem, leaves, flowers, pollen, and the water in the vase. It causes kidney failure in under three days. The toxin has still not been identified.
How much matters: There is no safe amount. Licking a few pollen grains off her fur while grooming is enough. If treatment is delayed 18 hours or more, kidney failure is generally irreversible. Lilium and Hemerocallis: Asiatic, Easter, Japanese Show, Oriental, Stargazer, Tiger, Wood and daylily.
This is the single most dangerous common houseplant for cats. Do not have them in the house.
SourceTheobromine and caffeine overstimulate the heart and nervous system. Signs start 6–12 hours after eating.
How much matters: Dose decides everything. Mild upset from about 20 mg/kg of methylxanthines, heart effects at 40–50, seizures at 60 or more. Merck's rough household rule is roughly 1 oz of chocolate per lb of body weight as a lethal quantity. Type matters far more than most people think: cocoa powder carries 28.5 mg/g and baking chocolate 15.5, against 5.3 for dark, 2.3 for milk and 0.04 for white.
SourceTartaric acid builds up in the kidney tubules because dogs lack the transporters other species have. Vomiting at 6–12 hours, kidney failure within 24–72.
How much matters: More than one grape or raisin per 10 lb of body weight may be enough.
Established in dogs. There are anecdotal reports in cats but no published case reports.
SourceSulfur compounds damage red blood cells. The anemia starts within 24 hours and peaks around 72, so an animal can look fine the first evening.
How much matters: Cats are the most susceptible species, then dogs. Less than a teaspoon of cooked onion, or 5 g/kg raw, can do it in a cat; dogs need 15–30 g/kg raw. Garlic is 3 to 5 times more toxic than onion gram for gram. Powdered and dehydrated forms in stock cubes, stuffing mix and baby food are the usual culprits.
SourceSame drug family as chocolate. Racing heart, tremors, restlessness, seizures.
How much matters: About 9 mg per lb of body weight. Three teaspoons of instant coffee grounds is enough for moderate signs in a medium dog. Used grounds and diet pills are concentrated sources.
SourceVomiting, diarrhea, loss of coordination, depressed breathing, tremors, blood pH changes, coma.
How much matters: No published threshold. Includes unbaked dough and fermenting fruit as well as drinks.
SourceTwo problems at once. The dough keeps rising in a warm stomach and can twist it, and the fermentation produces ethanol. Merck notes death is usually from the alcohol rather than the bloating.
How much matters: No threshold given.
SourceSodium poisoning. Vomiting, wobbliness, excessive thirst, then tremors and seizures in bad cases. Salt-dough Christmas ornaments are a repeat offender.
How much matters: No fixed threshold. Note that salt should never be used to make a pet vomit, for this exact reason.
SourceNot poisoning — cooking dries bone out and makes it brittle, so it splinters. The FDA logged obstructions, choking, mouth and tonsil cuts, rectal bleeding and around 15 deaths.
How much matters: Raw bones carry their own risks, mainly bacteria and fractured teeth. But cooked being safer than raw is backwards.
SourceLarge amounts cause disorientation, a racing heart, raised blood pressure and sometimes seizures, lasting up to 48 hours.
How much matters: The amount used in a recipe is very unlikely to cause more than mild stomach upset. The risk is a pet getting into the spice jar.
SourceCycasin causes vomiting, then liver failure and death. Every part is toxic and the seeds are the worst.
How much matters: No threshold given. Sold as a houseplant and used in landscaping in warm states, and badly underestimated.
SourceRicin. Severe gut signs, organ failure, death.
How much matters: Chewing and swallowing 1 to 2 seeds can be enough. The smallest lethal quantity on this page.
SourceTaxine alkaloids stop the heart. Often the first sign is sudden death. Merck's assessment is blunt: treatment is usually futile once signs appear.
How much matters: No threshold given.
SourceOleandrin, a cardiac glycoside, right through the plant. Vomiting, then an irregular heart rhythm, weakness and collapse.
How much matters: No threshold given.
SourceDigitoxin and digoxin — the same drug class used to treat heart failure, at the wrong dose. Abdominal pain, bloody diarrhea, slow irregular pulse, convulsions.
How much matters: No threshold given.
SourceColchicine. Gut signs, then kidney and liver failure, shock, blood cell damage and death.
How much matters: Not the same plant as the ordinary spring crocus, which only causes mild drooling and an upset stomach. Autumn crocus flowers in the fall and is far more dangerous.
SourceGrayanotoxin interferes with the heart and nerves. Vomiting, diarrhea, weakness, cardiac failure.
How much matters: No threshold in the ASPCA or Pet Poison Helpline entries.
SourceLeaves and flowers cause drooling and vomiting. The tuber underground is the dangerous part — large ingestions cause heart rhythm problems, seizures and death.
How much matters: No threshold given beyond large ingestions of tubers.
SourceLycorine. Small amounts do little; large ones cause vomiting, abdominal pain, dehydration and electrolyte problems. The bulb is the most poisonous part.
How much matters: No threshold given.
SourceTulipalin A and B, concentrated in the bulb. Vomiting, drooling, diarrhea, depression.
How much matters: No threshold given.
SourceCalcium oxalate crystals. Immediate pain, swollen tongue and throat, difficulty breathing. Merck also lists kidney failure for this one, which is unusual in this plant group.
How much matters: No threshold given.
SourceCalcium oxalate crystals plus unidentified proteins. Immediate burning pain in the mouth and throat. Deaths are rare mainly because the pain stops them eating more.
How much matters: No threshold given.
SourceCalcium oxalate crystals. Immediate mouth pain, drooling, gagging. Merck records no systemic reaction from insoluble calcium oxalate.
How much matters: Peace lily is not a true lily and does not cause kidney failure. Neither does calla lily. Unpleasant, not deadly.
SourceAnthraquinone glycosides in the latex, not the clear gel. Sudden severe diarrhea, sometimes vomiting.
How much matters: No threshold given.
SourceVomiting, depression, loss of coordination. The ASPCA does not identify the toxic compound.
How much matters: No threshold given.
SourceHederin in the leaves and berries, poorly absorbed. Abdominal discomfort and diarrhea, and only after a large amount.
How much matters: No threshold given.
SourceTurns into oxalic acid, which forms crystals in the kidneys. Looks like drunkenness for the first few hours, then kidney failure. Dogs take 36–72 hours to reach that stage, cats 12–24.
How much matters: Minimum lethal dose is 1.4 mL/kg for cats and 4.4–6.6 mL/kg for dogs. For a 9 lb cat that is under a teaspoon.
SourceCats cannot break permethrin down — their livers lack the enzyme capacity. It builds up in nervous tissue and causes tremors, seizures and death.
How much matters: Dog spot-on products run 45–60% permethrin. Cat-safe products are under 0.1%. That is a 450 to 600-fold difference. A cat can also be poisoned just by grooming a dog that was treated recently, without ever being treated herself.
Never put a dog flea treatment on a cat, and keep them apart for a day or two after treating the dog.
SourceCats cannot process it. It turns their blood brown so it stops carrying oxygen properly, and kills liver cells. Red blood cell damage within hours.
How much matters: Toxic dose in cats is usually 40–50 mg/kg, but signs have been reported at 10 mg/kg. One regular 325 mg tablet can be enough to kill an average cat. There is no safe dose.
SourceStrips the protective lining from the stomach and damages the kidneys.
How much matters: In dogs: stomach ulcers from 8–16 mg/kg a day, kidney failure risk at 175–300 mg/kg, potentially lethal above 600. Cats react at roughly half the dose dogs do.
SourceFive different chemical classes, each needing different treatment. Anticoagulants stop blood clotting, sometimes days later. Bromethalin swells the brain. Cholecalciferol raises calcium and wrecks the kidneys. Phosphides release toxic gas in the stomach.
How much matters: Merck is explicit that you cannot identify the type from the color or shape of the bait. Take the packaging to the vet — the treatment depends on which one it is.
SourceCats lack the liver enzyme for many of these and are especially sensitive to phenols. Drooling, vomiting, tremors, breathing trouble, liver failure.
How much matters: Named as dangerous to cats: wintergreen, sweet birch, citrus (d-limonene), pine, ylang ylang, peppermint, cinnamon, pennyroyal, clove, eucalyptus and tea tree. Active ultrasonic diffusers are worse than reed or heat diffusers because they put actual oil droplets in the air, which land on the coat and get swallowed during grooming.
SourceDestroys red blood cells. Vomiting and lethargy first, then anemia, jaundice and dark urine days later.
How much matters: A post-1982 US penny is 97.5% zinc, about 2,440 mg. Also galvanised nails, zippers, board game dice and zinc-coated tinsel.
SourcePaint chips, glazed pottery bowls, caulk, linoleum and the foil on wine bottles. Abdominal pain and vomiting, then behavior changes, tremors and seizures.
How much matters: A paint chip the size of a thumbnail can hold 50–200 mg of lead. Young animals absorb up to half of what they swallow.
SourceOverstated. The ASPCA page on avocado does not mention cats at all, and for dogs describes mild vomiting and diarrhea from persin. The species genuinely at risk are birds, horses and rodents. The real hazards in a dog eating avocado are the pit, which can block the gut, and the fat content, which can set off pancreatitis in a sensitive dog. Neither is poisoning.
SourceBackwards. Merck puts garlic at 3 to 5 times more toxic than onion, gram for gram. It gets treated as a safe natural flea remedy precisely because people rate it below onion.
SourceIt is an intolerance, not a poisoning. Most adult cats lose the enzyme that digests lactose, so it ferments and causes cramping and diarrhea. Unpleasant, not dangerous.
SourceOnly the green parts. The ASPCA's own entry says ripe fruit is non-toxic — the solanine sits in unripe fruit, leaves and stems.
SourceBoth wrong, in opposite directions. The kidney-failure toxin is specific to true lilies (Lilium) and daylilies (Hemerocallis), and specific to cats. Peace lily, calla lily and Peruvian lily are unrelated plants that share a common name, and cause mouth irritation or mild stomach upset. Getting this the wrong way round either way is dangerous.
SourceBackwards. Cooking dries bone out so it splinters into shards. Raw bone stays more intact — though raw carries its own risks from bacteria and cracked teeth.
SourceOur first-week checklists cover what to move, cover or throw out before you bring a new pet into the house.