Kryptonite

In its most well-known form, kryptonite is a green, crystalline material that emits a peculiar radiation that weakens and sickens Superman, but is generally harmless to humans when exposed to it in short term. However, when it gets into their bloodstream it can poison them. There are other varieties of kryptonite such as red and gold kryptonite which have different but still generally negative effects on Superman.

Green
Green kryptonite weakens Superman and other Kryptonians. It can and will kill them with long-term exposure. Kryptonians under kryptonite exposure experience severe muscular weakness, usually to the point of collapse, and excruciating pain, with both conditions progressively intensifying. Kryptonians under kryptonite exposure usually develop a fever and eventually will lose consciousness before death.

Blue
Blue kryptonite weakens Bizarro Kryptonians and Antimatter universe Kryptonians in much the same manner as green kryptonite affects regular Kryptonians. Blue kryptonite is also used in creating the antidote to the bizarre effects of red kryptonite.