Acetaminophen (Paracetamol) poisoning in dogs and cats
Toxic agent: Acetaminophen / paracetamol · Reviewed 2026-08-18
Phone a vet now, before reading on. Have ready: your pet's weight, roughly how much was eaten and when, and the packaging if there is any. ASPCA Animal Poison Control (+1 888 426 4435), Pet Poison Helpline, or Animal PoisonLine in the UK.
One regular-strength tablet can kill a cat. Cats lack the enzyme that lets humans and dogs process this drug, and well-meaning owners giving a painkiller are a leading route to feline poisoning.
What it actually does
Humans detoxify acetaminophen mainly by glucuronidation. Cats have very little glucuronyl transferase, so the drug is shunted down an oxidative pathway that produces a reactive metabolite. In cats this oxidises haemoglobin into methaemoglobin, which cannot carry oxygen, and damages red cells; in dogs the same metabolite mostly kills liver cells. Two species, one drug, two different emergencies.
How much matters
The species gap here is wider than for anything else on this list:
| Cats | toxic from about 10 mg/kg — a single 500 mg tablet is roughly ten times a lethal dose for an average cat |
|---|---|
| Dogs | liver injury from about 100 mg/kg, methaemoglobinaemia at higher doses |
| Common tablet strengths | 500 mg in the UK, 325 or 500 mg elsewhere |
| Combination products | cold and flu remedies hide acetaminophen alongside decongestants that are toxic in their own right |
There is no safe home dose of acetaminophen for a cat. Not a quarter tablet, not a children's suspension.
What you will see, and when
Onset: Cats: 1–4 hours. Dogs: liver signs at 24–72 hours.. Typical course: Treatment typically runs 24–72 hours.
- 1–4 hours (cats)Brown or muddy gums, laboured breathing, facial and paw swelling, drooling, dark urine
- 4–12 hoursWeakness, collapse, brown-tinged blood as methaemoglobin rises
- 24–72 hours (dogs)Vomiting, abdominal pain, jaundice, liver failure
What the vet will do
This one has an antidote, which is why speed pays. N-acetylcysteine restores the glutathione the liver has burned through, and it works best given early. Add oxygen, intravenous fluids, sometimes ascorbic acid, blood transfusion in severe methaemoglobinaemia, and liver support in dogs.
Outlook
Good in cats treated within a few hours. Poor once a cat is deeply cyanotic or a dog is in liver failure.
Dogs and cats are not the same here
Cats are the emergency. Dogs are far more tolerant but not safe, and neither should ever receive it without veterinary instruction.
Where it comes from in a normal house
- Paracetamol and Tylenol tablets
- Cold, flu and sinus combination remedies
- Children's liquid paracetamol
- Prescription co-codamol and similar combinations
- Handbags, bedside tables and dropped tablets
The thing people get wrong
“It is safe for children, so a small dose must be safe for a cat.”
The reason it is safe for children is an enzyme cats do not have. Body weight is not the variable that matters here — metabolism is. Human painkillers should never be given to a cat, and paracetamol is the least forgiving of them.
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Get PawLife on the App StoreFrequently asked questions
How much Acetaminophen (Paracetamol) is dangerous?
There is no safe home dose of acetaminophen for a cat. Not a quarter tablet, not a children's suspension.
How long after exposure to Acetaminophen (Paracetamol) do symptoms start?
Cats: 1–4 hours. Dogs: liver signs at 24–72 hours.. Brown or muddy gums, laboured breathing, facial and paw swelling, drooling, dark urine. Treatment typically runs 24–72 hours.
Is Acetaminophen (Paracetamol) worse for cats or dogs?
Cats are the emergency. Dogs are far more tolerant but not safe, and neither should ever receive it without veterinary instruction.
Is it true that: It is safe for children, so a small dose must be safe for a cat.
The reason it is safe for children is an enzyme cats do not have. Body weight is not the variable that matters here — metabolism is. Human painkillers should never be given to a cat, and paracetamol is the least forgiving of them.
Related emergencies
Sources
This page is information, not veterinary advice. Toxic doses vary with body weight, age, breed and individual sensitivity, and the figures above exist to explain what a vet is assessing, never to decide that an amount is safe. If you are reading this because something has already been eaten, call a vet.