Is painkillers one or two words?

in reference to a pill, one word.

One

If you are using it in reference to a medication, it is one word. painkiller - no hyphen

Painkiller (pain killer) I think is actually one word. Unless your using it in a special occasion which you probably aren't.

One, for medical references.

one word

one word (do you see a hyphen that would say it is two?

two

one word. trust me!!! it's in da dictionary!!

one word!

good luck. :)