I don't know where the "no painkillers" meme comes from, but opium's been around forever and is among the easiest drugs to harvest: just lightly score the poppy seed pod and collect the latex. It was as known and available in the middle ages as in the ancient Greek world.

https://www.neurology.org/doi/10.1212/WNL.92.15_supplement.P...

Alcohol, though, is great for dissolving opium into an easily ingestible potion, whence one gets dwale or laudanum.