a painkiller once ingested sends a type of sedative through your body which eventually reaches your brain which sends signals to your nervous system causing the irritated nerves to become less and less irritated. the reason they take so long to kick in is because they have to work through your body via the bloodstream
hope this helps :) ❤❤❤❤❤❤❤❤❤❤❤❤❤❤❤❤❤❤❤❤