The following list contains a variety poisons and venom's that can normally can kill or seriously harm us, but... are also used as medicines by doctors and pharmacists around the world:
Warfarin
Snail Venom
Wolfsbane
Digitalis
Copperhead Venom
Hemlock
Deadly Nightshade
Scorpion Venom
Tarantula Venom
Ergot
That being said, I doubt bleach warnings count for much in a society with a long history of using poisons to cure people.