This American Life had a good 2013 episode on the tricky dosing of acetaminophen [1]. It's also worth saying that capsaicin is used for pain relief[2]! Especially for things like muscle and joint pain.

[1] https://www.thisamericanlife.org/505/use-only-as-directed

[2] https://my.clevelandclinic.org/health/drugs/18080-capsaicin-...