Does kryptonite have the same effect on humans as it does on superman or is it only harmful on Superman because he is from Krypton? I only ask because I know that it's a radiation.
It doesn't have the same effect, but it CAN effect humans. Lex Luthor once wore a Kryptonite ring and after a few months he had to amputate his hand because of the radiation.
No, and you know the real reason Kryptonite affects Superman the way it does? It's because the Writers had to give him at least ONE weakness, or it would get boring.