NSAIDs (Ibuprofen, Naproxen, Aspirin)

How Much Is Dangerous

Cats are markedly more sensitive to NSAIDs than dogs, and there is essentially no established safe recreational or accidental dose. Even the doses sometimes used therapeutically under close veterinary supervision — such as carefully-spaced, low-dose aspirin occasionally used for certain feline heart conditions — require unusually cautious, infrequent dosing schedules specifically because of how slowly cats clear the drug compared to other species. A single adult-strength ibuprofen or naproxen tablet, an amount that would be a normal human dose, can cause serious illness in a cat.

Symptoms

• Vomiting, sometimes containing blood
• Loss of appetite
• Abdominal pain, sometimes evident as a hunched posture or reluctance to be touched around the belly
• Black, tarry stool — a specific sign of gastrointestinal bleeding/ulceration higher up in the digestive tract
• Lethargy
• Increased thirst and urination initially, progressing to reduced urination as kidney injury develops — following the same general pattern seen with other nephrotoxic exposures on this list
• Seizures or coma in severe overdoses

Time to Symptoms

Gastrointestinal signs can begin within hours of ingestion; kidney injury, the more medically significant longer-term consequence, typically develops over the following 1–3 days as the reduced blood flow and prostaglandin-blocking effects accumulate.

First Aid Steps

• Treat any human NSAID ingestion by a cat as an emergency and contact a veterinarian or emergency animal hospital immediately
• Never give a cat any human pain reliever, including "just one dose" offered out of concern for apparent pain or fever — safe, appropriately-dosed prescription options genuinely exist for cats and should always come from a veterinarian rather than a human medicine cabinet
• Bring the medication packaging to help the treating team calculate the exact dose ingested, which meaningfully informs the treatment plan and monitoring intensity

What Not To Do

• Do not give any NSAID to a cat without specific veterinary direction — this remains one of the most common and most genuinely preventable sources of serious feline drug toxicity seen in veterinary practice, precisely because these medications are so commonly kept in human households and seem, incorrectly, like a reasonable thing to share
• Do not assume that a smaller, "cat-sized" fraction of a typical human dose is automatically safe — cats' notably slow clearance of these drugs means even small fractional doses can accumulate to genuinely toxic levels, particularly with any repeated dosing over more than a single instance

Veterinary Treatment

Decontamination if caught early after ingestion (induced vomiting, activated charcoal), medication to protect the remaining healthy stomach lining (such as a proton pump inhibitor or sucralfate) to limit further ulceration while the drug clears, and IV fluid therapy to support kidney function and blood flow during the vulnerable period. Bloodwork monitoring for kidney values and evidence of ongoing GI bleeding continues over several days given how the effects unfold over time rather than resolving immediately. Prognosis depends heavily on both the specific dose ingested and how quickly treatment began after exposure.

Toxic Compound

NSAIDs — ibuprofen, naproxen, aspirin, and similar drugs — work by inhibiting the production of prostaglandins, signaling molecules that, among other functions, protect the stomach lining from its own acid and maintain adequate blood flow to the kidneys. Blocking prostaglandin production therefore causes both gastrointestinal ulceration and kidney injury as predictable, mechanism-based consequences rather than unusual side effects. Cats' reduced activity of the liver enzyme glucuronyl transferase — the same underlying trait behind their acetaminophen sensitivity — also means aspirin specifically is cleared far more slowly in cats than in dogs or humans: its half-life in cats is roughly 37.5 hours, compared to just a few hours in most other commonly-treated species, meaning repeated dosing accumulates dangerously in a way it wouldn't in a dog given the same schedule.