- Very toxic — even tiny amounts
- Within hours
- Affects: Stomach & kidneys
Why this verdict for dogs
Naproxen (Aleve) is an especially potent NSAID with a very narrow safety margin in dogs — small amounts can cause stomach ulcers and kidney failure.
Warning signs to watch for
- Vomiting, sometimes bloody
- Black, tarry stool
- Loss of appetite
- Increased thirst & urination
⚠ If your dog ate naproxen (aleve)
Act immediately — don't wait for symptoms.
- Call your vet or a pet poison helpline right away.
- Note how much was eaten and when.
- Do not induce vomiting unless a professional tells you to.
Naproxen — sold as Aleve or Naprosyn — deserves to be singled out from the other human painkillers, because it is the one that does the most damage at the smallest dose in dogs. Vets treat it with more alarm than ibuprofen, and owners are usually surprised by that.
How much is safe?
Never give it, in any amount. The reason naproxen is so dangerous to dogs is that they clear it extraordinarily slowly — a dose that a human body processes in hours can circulate in a dog for more than a day, so the damage keeps accumulating. Stomach ulceration has been reported at doses as low as around 5 mg/kg, which means a single standard 220 mg tablet is a serious exposure for a medium-sized dog and a potentially critical one for a small breed. Cats are more sensitive still.
What happens if a dog eats too much?
The stomach and small intestine are attacked first: vomiting that may contain blood or look like coffee grounds, black tarry stool, appetite loss and abdominal pain. Kidney injury follows, showing as increased or decreased urination and worsening lethargy. Because the drug lingers, a dog can appear to stabilise and then get worse again, and ulcers can perforate days after the original tablet.
⚠ What to do if your dog ate naproxen (aleve)
This is a call-now situation even for one tablet. Contact your vet or a poison line (ASPCA 888-426-4435 · Pet Poison Helpline 855-764-7661) with the tablet strength, how many are unaccounted for and your pet's weight. Treatment usually involves decontamination if it is recent, then several days of stomach protection and IV fluids — longer than for other NSAIDs precisely because the drug hangs around. Take the bottle with you.
⚠️ Worried your pet got into this?
Frequently asked questions
Why is naproxen worse than ibuprofen for dogs?
Mainly the half-life. Dogs eliminate naproxen extremely slowly, so a single dose keeps causing harm for a day or more instead of clearing overnight.
My dog ate one tablet and vomited it up — are we clear?
Not necessarily, and a dog vomiting after an NSAID may already be showing an effect rather than clearing the drug. Call regardless.
More medications for dogs
By the CanMyPet Editorial Team · Reviewed against ASPCA Animal Poison Control, the American Kennel Club (AKC) and Pet Poison Helpline · Last updated July 31, 2026.
Sources
- ASPCA — People Foods to Avoid Feeding Your Pets
- American Kennel Club — Dog Nutrition
- Pet Poison Helpline — Poison List