My dog ate Tylenol.
How serious?
Acetaminophen (Tylenol, paracetamol) has no vet-recommended home use in dogs. Severity depends on mg per kg. Cats: any amount is an ER trip, skip the math and see the cat page.
Brown gums, labored breathing, or a CAT involved? Call 855-764-7661 NOWPublished thresholds (dogs)
Liver injury (hepatotoxicity) is reported from about 100 mg/kg in dogs. Blood toxicity (methemoglobinemia, brown gums, labored breathing) is reported from about 200 mg/kg. One 500 mg extra-strength tablet crosses 100 mg/kg for any dog under about 11 lb. Cats are a different story entirely: no safe dose exists at any weight.
Why cats are different
Cats lack the liver pathway that processes acetaminophen, so even part of one tablet can be lethal. If a cat is involved, skip this calculator and go to the cat emergency page.
What NOT to do
Do not give any "counteracting" human medication. Do not induce vomiting without professional direction. Do not re-dose "to help with pain": vet-prescribed pain control exists for dogs, and acetaminophen is not it.