Is Naproxen toxic to cats?
No. Naproxen is an NSAID with an especially long half-life in cats — it stays toxic in the system far longer than other NSAIDs.
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Content compiled with reference to guidance from the Blue Cross, PDSA, Royal Veterinary College (RVC), Battersea, and Animal PoisonLine. This site does not provide veterinary advice — always consult a vet. Last reviewed: 27 September 2026.
Key facts
- Verdict: No — dangerous to cats. Naproxen should never be given deliberately.
- Category: Human painkiller
- Onset: Signs can start 0–6 hours — see the full timeline below.
- If it's already happened: Call your vet now, or the Animal PoisonLine on 01202 509000 (24/7, charges apply) — see the emergency steps below.
If your cat has just eaten naproxen
- Move your cat away from any remaining naproxen. Do not try to make them vomit at home — this is dangerous in cats and rarely works.
- Note how much was eaten and when, and keep the packaging or a photo of the plant/substance if you can.
- Call your vet immediately, even out of hours. Tell them your cat's weight, what they ate, and when.
- If you can't reach your vet, call Animal PoisonLine (01202 509000) — paid triage, 24/7 for guidance. They can advise on urgency and route you to emergency care.
What's the full picture?
Naproxen (UK brand Naprosyn and in some Nurofen Joint & Back products) is an NSAID that causes severe toxicity in cats at tiny doses.
Symptoms include vomiting (often bloody), abdominal pain, and — within 24-72 hours — acute kidney injury. Signs can be subtle at first.
Never give any NSAID to a cat. If you suspect exposure, go to the vet immediately — treatment is most effective in the first few hours.
Symptoms to watch for
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Cat owner essentials
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Questions owners ask
How much naproxen is dangerous to a cat?
Naproxen causes severe toxicity in cats at very small doses compared to some other NSAIDs, partly because of its especially long half-life in feline metabolism — it stays active in the body far longer than ibuprofen or aspirin. A single tablet, even a low-strength one, should be treated as a serious poisoning risk.
Why is naproxen considered more dangerous than other NSAIDs for cats?
The long half-life is the key issue — while cats struggle to clear most NSAIDs efficiently, naproxen persists in their system for an especially long time, meaning the toxic effects build up and last longer than with a shorter-acting NSAID at an equivalent dose. This also means recovery and monitoring periods tend to be longer than with other painkiller exposures.
How soon would symptoms appear, and how long do they last?
Early signs — vomiting, drooling, loss of appetite — typically appear within 6 hours. GI bleeding and reduced urine output can follow at 6–48 hours, with acute kidney failure and anaemia from blood loss developing over 2–5 days. Given the drug's long half-life, monitoring and treatment often need to continue longer than with a shorter-acting NSAID exposure — follow your vet's guidance on follow-up bloodwork even after initial treatment.
A lockable medicine box is the simplest way to keep human tablets out of reach of a curious cat.
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Related
Sources referenced for this guidance
- Veterinary Poisons Information Service (VPIS) — UK clinical toxicology reference used by vets
- International Cat Care — feline-specific clinical guidance
- BSAVA — British Small Animal Veterinary Association reference materials
- Merck Veterinary Manual — professional veterinary reference
About this guidance
Every entry on this site is compiled from published UK veterinary toxicology sources — International Cat Care, Veterinary Poisons Information Service (VPIS) references, RCVS-registered practice materials, and peer-reviewed feline medicine literature. Where the evidence is mixed, we err on the cautious side because cats are unusually sensitive to many common substances that are harmless to humans and even to dogs.
This is general information written for UK cat owners. It is not personalised veterinary advice for your specific cat, their age, weight, medical history, or the exact exposure you're dealing with. If your cat has eaten something or is unwell, call your vet first. The Animal PoisonLine on 01202 509000 is available 24/7 for a small fee and can tell you whether an emergency visit is needed.
Entries are reviewed and updated as new research emerges. Spotted an error? Let us know — corrections are investigated and applied within 24 hours. For more context on how we work, see about and our full disclaimer.
Last reviewed: · By the What Can My Cat Eat? editorial team