Sith poison was a biological toxin, and a product of Sith alchemy, that when absorbed in sufficient quantity, multiplied the rage felt by a person. In action it was more of a disease, taking up residence in the victim's body and setting off chemical reactions that rapidly diminished the victim's ability to resist the pull of the dark side of the Force. The poison could be fatal unless counteracted by strong Jedi powers, and even then its effects were likely to remain.