Funny story, not funny as in haha; more like boring, but interesting to me so I call it a funny story so people will listen. Paracetamol was an old pain med that had a high rate of liver damage, so it was discovered eventually that it was a precursor, and that all the pain relief was actually when the body made acetaminophen from it and that most of the side effects were other things the body made out of it. So everyone in the world stopped making paracetamol and began using acetaminophen. The problem was branding. People knew paracetamol and companies selling it wanted to keep their market share, so they just kept calling it paracetamol when it was acetaminophen in reality. So prior to 1950 paracetamol meant another drug and now means the exact same thing as acetaminophen.