Kryptonite

Kryptonite is a radioactive mineral that made up most of the planet Krypton's structure, including its core

The effects of the kryptonite on Kryptonians can be shielded or blocked with lead. Also, some Kryptonian technology can neutralize the effects of kryptonite. LuthorCorp was able to develop a technology to absorb the radiation of the kryptonite.

Green kryptonite emits a radiation that is extremely toxic to super-powered Kryptonians. The radiation itself first causes symptoms such as nausea, dizziness, pain, and weakness that eventually grow more severe until loss of consciousness occurs. Green kryptonite can also affect humans, causing mutations and psychosis