Never give a cat acetaminophen (Tylenol) without the advice of your veterinarian. Cats are unable to metabolize the drug resulting in toxic effects. As little as one tablet can be lethal to a cat.
Most cats that are exposed to acetaminophen by either from accidentally ingestion of an improperly stored drug or by well-meaning owners giving their cats an incorrect dose.
Don't give your cat any medication unless directed by your veterinarian.
Acetaminophen toxicity may cause vomiting, diarrhea, trouble breathing, abnormal color to gums (brown color instead of pink), swelling of the face, lips, limbs, weakness, lethargy, and/or liver failure.
For more information please read AcetaminophenToxicity in Cats.