Many drugs containing opiates are mixed with acetaminophen[1] by drug companies to reduce their abuse potential as acetaminophen is very toxic. The thought is that people that would abuse these medicines would think twice. All it really does is kill people[2] to the point where the government puts out information on how to spot someone going through such a poisoning.

[1] https://www.physicsforums.com/threads/why-some-opiates-mixed... [2] https://www.nlm.nih.gov/medlineplus/ency/article/002670.htm

Even worse, acetaminophen has some serious difficulty with water solubility, so the people who really want the APAP out can get it done with no special equipment whatsoever. I wish combination drugs would just go away across the board, in all honesty.

Many common opioid formulations contain acetaminophen (paracetamol) in large amounts. If addiction develops, the acetaminophen will be the thing that kills you, via fulminant hepatic failure.