Basically, painkillers and maybe the placebo effect.
More wars, more brave stunts, more willingness to take risks, more torture but the torture will be less effective. Maybe more scepticism about medicine because the placebo effect affects how medicines work.
Kingdoms try to expand but their enemies try harder to resist so it results in a stalemate, so not that much real change, maybe, at least politically.
http://en.wikipedia.org/wiki/Endorphin