Toxic or Not?
Answer: Toxic to cats in any dose, toxic for dogs at higher levels.
Tylenol (acetaminophen} is highly toxic to cats. Just 46mg/kg body weight is enough for a cat to show signs and one 325mg pill may kill an average 10 lb. cat, if not treated quickly. While dogs may be able to tolerate doses of up to 50 to 100mg/kg body weight, acetaminophen should only be given to dogs under veterinary supervision, and dosed cautiously in dogs with underlying liver disease or who are on any other medications that affect their livers. Doses of 200mg/kg (4 extra-strength 500mg tablets in a 20 lb. dog) or higher are definitely toxic to dogs.
Signs of acetaminophen poisoning are blue or brown gum color from lack of oxygen and methemoglobin formation, difficulty breathing, facial swelling (a hallmark sign), lethargy, low body temperature, and vomiting. May progress to weakness, coma, and death from liver failure if untreated.
While dogs may accidentally consume human medications, acetaminophen toxicity in most pets is usually caused by well-meaning owners giving over the counter medications to their pets. Remember that acetaminophen can be found in many over the counter (OTC) medications, both those bearing the Tylenol brand name and in many other brands and generics. Never give any OTC human medications to your pet without consulting with your vet first.