One of the most widely prescribed drugs in history works by mechanisms which have not yet been agreed upon by the medical establishment. It‘s believed that paracetamol acts via more than one neurological pathway, one of which may be by inhibiting the COX-3 isoform of the COX family of enzymes. Ref. wikpedia
“The fact is, despite its ubiquity, we still don’t really understand how paracetamol works. A leading theory is that, in part, it works like aspirin and ibuprofen, by blocking enzymes known as cyclooxygenases.
These enzymes are responsible for making hormone-like compounds called prostaglandins, which trigger pain and swelling in the body as well as stimulating production of the mucous that shields our stomachs against digestive acids.” source: see below
Recent research suggests that Paracetamol has a marginal effect for pain relief - but only in around 25% of individuals - and that its beneficial action in others is due to placebo effects. However, the drug has significant side-effects (including stomach-lining damage) and overdoses each year run into 80,000 per year in the US alone.
A May 2014 cover story from New Scientist 'Cure-all no more' drew attention to a review of research that looked at people taking paracetamol to relieve chronic joint pain, examining seven studies that compared the drug with a placebo. Five of these found it to be marginally more effective, but two found no difference.
“Why are we bothering to give a drug to people that’s toxic, that has significant potential problems, when it doesn’t work?” asks Andrew Moore, an anaesthetist and director of pain research at the University of Oxford. “It’s unethical.”