I didn’t know this until recently either. I grew up on a family where if there was pain, you just take tylenol to deal with it. We always followed the dosage timing and never had issues. So recently when my wife had some chronic pain I suggested taking tylenol but even after two days the pain would not go away and she went to ER. They did a blood check to see if they could find anything. They didn’t find the cause, just suspected food poisoning, but they found her liver enzymes were near dangerous levels. This was even with timing the dosages absed on instructions. Now I am super careful wtih Tylenol.