How many mg of tylenol (acetaminophen) does it normally take for an overdose to be lethal?

Depends: Generally, one should not take more than 4g/day of all tylenol (acetaminophen) sources (assuming your liver is normal - less, if abnormal). However, it all depends on one's metabolism, liver health, and period of time over which the ingestion occurred. The attached diagram shows what the dr does - look at the plasma level (blood test) to determine the toxicity (plus other blood markers of liver disease).

7000 mg : A person should not take more than 4000 mg a day and that is still a very high dose. 7000 mg can be lethal. Symptoms include nausea, vomiting, jaundice, irritability, coma, convulsions, diarrhea and abdominal pain ( this is not a complete list). Immediately go to a hospital if you or someone you know may have overdosed. And if you are suididal you need to see a professional immediately.