How a cat's metabolism turns aspirin deadly
Cats lack enzymes to efficiently process salicylates, so aspirin lingers in their system far longer than in humans or dogs. That half-tablet could still be circulating in your cat's bloodstream today, risking ulcers or kidney damage. Even if they seem fine now, internal bleeding might not show outward signs until it's advanced.
Watch for subtle changes like decreased appetite or hiding—cats often mask pain until it's severe. Dark, sticky vomit or unusually pale gums indicate bleeding. Blood tests can reveal anemia or elevated kidney values, but waiting for these signs reduces treatment options. Yesterday's ingestion means inducing vomiting won't help, but vets can still provide supportive care.
Why delayed symptoms are especially dangerous
Unlike dogs that often vomit soon after NSAID ingestion, cats may take 24-48 hours to show distress. By then, kidney damage could be underway. Your vet might hospitalize your cat for IV fluids to maintain blood flow to the kidneys and administer medications to protect the stomach lining.
Recovery depends on the dose relative to your cat's weight and how quickly treatment starts. A 325mg tablet is a massive dose for most cats—for context, veterinary aspirin doses for cats (when absolutely necessary) are typically under 10mg per kg, given only under direct supervision. Never assume human medications are safe just because they're sold over-the-counter.
For a dose worked out against your pet's weight, use the Aspirin Toxicity Calculator.