Paracetamol poisoning, also known as acetaminophen poisoning, is caused by excessive use of the medication paracetamol (acetaminophen). Most people have few or non-specific symptoms in the first 24 hours following overdose. This may include feeling tired, abdominal pain, or nausea. This is typically followed by a couple of days without any symptoms after which yellowish skin, blood clotting problems, and confusion occurs. Additional complications may include kidney failure, pancreatitis, low blood sugar, and lactic acidosis. If death does not occur, people tend to recover fully over a couple of weeks. Without treatment some cases will resolve while others will result in death.

Based on this passage, most serious toxic effect of acute acetaminophen overdose? Let's think fast. Stream of consciousness:
The relevant information to answer the above question is: If death does not occur, people tend to recover fully over a couple of weeks. So the final answer is death.