Naproxen poisoning in dogs and cats
Toxic agent: Naproxen, a long-acting NSAID · 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.
Naproxen is the NSAID that catches people out. It is toxic to dogs at a fraction of the ibuprofen dose because they cannot clear it — the half-life in a dog is around three days.
What it actually does
The same COX inhibition as ibuprofen, but the pharmacokinetics are what make it dangerous. Humans clear naproxen in roughly 14 hours; dogs take about 74. The drug recirculates through the liver and gut repeatedly, so a single tablet keeps working on the stomach lining for days.
How much matters
Compare the numbers with ibuprofen and the difference is stark:
| From about 5 mg/kg | gastrointestinal ulceration in dogs |
|---|---|
| From about 25 mg/kg | kidney injury |
| One 220 mg tablet in a 10 kg dog | 22 mg/kg — four times the ulcer threshold |
| Half-life in dogs | about 74 hours, against 14 in humans |
This is the entry where the dose that matters is genuinely one tablet. Naproxen ingestion in a dog is an emergency at quantities that sound trivial.
What you will see, and when
Onset: Hours, but signs can appear days later because of the persistence. Typical course: Monitoring and gastroprotection for up to a week.
- HoursVomiting, drooling, abdominal pain
- 1–3 daysMelaena — black tarry stools — anaemia, weakness
- 3–7 daysKidney injury, and ulcers that continue to develop as the drug recirculates
What the vet will do
Aggressive decontamination including repeated activated charcoal, because enterohepatic recirculation means charcoal keeps having something to bind. Then prolonged proton pump inhibitor and sucralfate therapy, fluids, and blood work over several days rather than one.
Outlook
Good with early and sustained treatment. The cases that go badly are the ones treated as a single-day problem.
Dogs and cats are not the same here
Dogs are the usual patient and the poor clearance is a canine trait. Cats are also highly susceptible.
Where it comes from in a normal house
- Aleve, Naprosyn, Feminax Ultra
- Prescription naproxen for arthritis and back pain, often in large bottles
- Bedside tables and pill organisers
The thing people get wrong
“It is the same class as ibuprofen, so the same amount is roughly the same risk.”
Same class, different clearance. A dog needs about a tenth of the ibuprofen dose of naproxen to ulcerate, and the drug is still active three days later. Treat any naproxen ingestion as more serious than the equivalent ibuprofen.
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Get PawLife on the App StoreFrequently asked questions
How much Naproxen is dangerous?
This is the entry where the dose that matters is genuinely one tablet. Naproxen ingestion in a dog is an emergency at quantities that sound trivial.
How long after exposure to Naproxen do symptoms start?
Hours, but signs can appear days later because of the persistence. Vomiting, drooling, abdominal pain. Monitoring and gastroprotection for up to a week.
Is Naproxen worse for cats or dogs?
Dogs are the usual patient and the poor clearance is a canine trait. Cats are also highly susceptible.
Is it true that: It is the same class as ibuprofen, so the same amount is roughly the same risk.
Same class, different clearance. A dog needs about a tenth of the ibuprofen dose of naproxen to ulcerate, and the drug is still active three days later. Treat any naproxen ingestion as more serious than the equivalent ibuprofen.
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.