Presumably yes, and for historical context look to Napoleon Bonaparte. It's presumed that when he attempted suicide the mercury cyonide had "expired" (humidity and water got in) and that's why his suicide failed. I still wouldn't go around eating expired poison to prove a point though.
Surely it'd be less effective since some of the molecules or whatever have broken down into (hopefully) less poisonous molecules?
Presumably yes, and for historical context look to Napoleon Bonaparte. It's presumed that when he attempted suicide the mercury cyonide had "expired" (humidity and water got in) and that's why his suicide failed. I still wouldn't go around eating expired poison to prove a point though.