/u/Corpcasimir hit it on the head. Acetaminophen would never make it to market today. The window between "this works" and "this kills you" is so small for that drug that it's scary that you can just buy it over the counter.

Whenever you take a drug, your body has mechanisms that "see" that it's not something your body has produced and is not food/nutrition. It will then take steps to modify that compound chemically to get it out of your body. For Acetaminophen, the majority of is is metabolized to something you can just pee out. A small amount of it is converted to something else though, something reactive and extremely toxic. Get enough Acetaminophen in your body, or even if you just happen to metabolize it more in the "bad" way, and you get this stuff building up. What literally happens is that it physically reacts with the proteins that control energy production in your cells. No way to make cellular energy = cells die. Enough cells die, your organs start to fail. So yeah. Don't take acetaminophen if you have any other option.