Green kryptonite, the only variety potentially fatal to Superman, induces lassitude and inertia followed by death if not removed in time from Superman's presence.
Green Kryptonite: The most common form of kryptonite. In superpowered Kryptonians, causes immediate physical pain and debilitation and kills within hours. Has no short-term effects on humans (though strictly in post-Crisis continuity, long-term exposure is apparently lethal to humans) or non-superpowered Kryptonians. In one early Silver Age story, Superboy built up immunity to specific chunks of green kryptonite through repeated non-fatal exposure, as seen in the story "The Great Kryptonite Mystery", (Superboy (volume 1) #58, July 1957). In most incarnations, lead blocks the effects of kryptonite.
