The FDA's page on pain relievers for pets answers this in one paragraph. Aspirin, ibuprofen (Advil, Motrin) and naproxen (Aleve) are anti-inflammatory drugs that in an animal may last longer, be processed differently, be absorbed faster, and reach higher blood levels than in a person. The result the FDA lists: ulcers in the stomach and intestines, holes in the stomach and intestines, kidney failure, liver failure, and in some cases death.
Cats are especially sensitive to these drugs, and acetaminophen (Tylenol) is in a class of its own: the FDA says it is fatal to cats, because a cat's liver lacks the enzymes needed to break it down.
The FDA lists the anti-inflammatory drugs it has approved for dogs: carprofen (Rimadyl), deracoxib (Deramaxx), firocoxib (Previcox), grapiprant (Galliprant) and meloxicam (Metacam). Each Petipedia page is written from the label, with what it warns about, and without doses.
For cats the list is short and the FDA is specific: meloxicam as a one-time injection, and robenacoxib (Onsior) for at most three days. No anti-inflammatory drug is approved for long-term use in cats. A cat in chronic pain is a conversation with the vet about the other options, not a shared bottle.
The approved drugs are the same class as ibuprofen. What is different is that they were tested in the species at a dose the species tolerates, and that the FDA lists the same organs, stomach, kidneys and liver, as the ones to watch even with the approved ones, which is why vets often run blood tests before and during a course. Vomiting, less appetite, diarrhea and less activity are the common side effects on those labels, and the reason the vet says to stop and call if they appear.
Petipedia's page on what the vet just prescribed has every one of them.
Read 18 September 2026.