Recently, This American Life did an episode on how easy it is to overdose on acetaminophen (also called paracetamol in countries outside of the US). You can listen to the entire episode in the link below:
What I find interesting is why this drug is so dangerous.
In the liver, there are a group of enzymes that oxidize many of the drugs and organic substances that enter your body. In fact, there are genes for 57 various types of these enzymes. These are called Cytochrome P450s.
Whenever you see warning labels like “don’t eat grapefruit with this drug,” it is usually because of the way the liver cytochromes are processing these compounds.
So, what happens when you take acetaminophen? Most of it is processed to a non-harmful compound. However, 5% of this drug is processed by a liver cytochrome known as CYP2E1. This 5% becomes a toxic compound (NAPQI). Generally, the liver can take care of this substance through a reaction with a compound known as glutathione. However, in cases of overdose, there is not enough glutathione to convert the bad NAPQI, and it hangs out in the liver and reacts with cellular membranes. Essentially, your liver cells are slowly killed.