Emergency Tool

Paracetamol toxicity calculator for cats

Work out the paracetamol dose your cat has received. In cats the toxic threshold is around 10 mg/kg — a single standard 500 mg tablet is 10–12 times that for an average-sized cat. In almost every case the answer is: go to the vet now.

Paracetamol poisoning is time-critical

Treatment within 2 hours of ingestion has the best outcome. If your cat has had any paracetamol, don't wait for this calculator's result — call your vet now. Use the calculator en route.

In the UK: your vet first, then the Animal PoisonLine on 01202 509000 (24/7, charges apply).

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Most adult UK domestic cats are 3.5–5.5 kg. Kittens and smaller breeds are at greater risk.

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How this calculator works

Cats lack a key liver enzyme (glucuronyl transferase) needed to process paracetamol safely. What converts to a toxic metabolite in humans and dogs in tiny amounts does so far more aggressively in cats. The toxic threshold in cats is roughly 10 mg/kg body weight — and the gap between 'toxic' and 'fatal' is small.

  • Under 10 mg/kg — below the documented toxic threshold, but this is not a 'safe' zone. Any exposure needs veterinary contact because cats cannot clear paracetamol the way humans can.
  • 10–50 mg/kg — moderate toxicity — methaemoglobinaemia (brown-grey gums), liver injury. Emergency.
  • 50–100 mg/kg — severe toxicity — high risk of death without aggressive treatment.
  • Over 100 mg/kg — often fatal even with treatment. Immediate emergency care only.

A single standard 500 mg paracetamol tablet in a 4 kg cat delivers 125 mg/kg — ten times the toxic threshold.

Signs of paracetamol toxicity in cats

0–4 hours
Loss of appetite, drooling, vomiting, lethargy.
4–12 hours
Brownish-grey gums (methaemoglobinaemia — blood can't carry oxygen), swelling of face and paws, rapid breathing.
12–48 hours
Jaundice, liver failure, collapse. Without treatment, mortality is very high.

Why this matters in the UK specifically

The UK is a liquid paracetamol country — Calpol is in most households with a child. It's sweet, it spills, and a syringe's worth is more than enough to kill a cat. Nearly every feline paracetamol emergency in the UK comes from one of three routes:

  • A caring owner giving 'just a little bit' for what they think is a cat in pain.
  • Calpol spilled on a floor, counter, or child's face that the cat then licks.
  • A paracetamol tablet dropped and not found — until the cat has eaten it.

Never treat a cat in pain with human medicine. Call your vet — safe feline painkillers exist and require a prescription.

If you're worried right now

Call your vet or out-of-hours emergency vet first. For poison advice, the Animal PoisonLine (UK) is on 01202 509000 — 24/7, charges apply.