Kryptonite

Kryptonite is a radioactive mineral from the planet Krypton. Following its destruction, some Kryptonite found its way to the planet Earth.

Green Kryptonite
Kryptonite is normally green and Kryptonians exposed to the element will become weak within close proximity or pierced by weapons laced or made from the substance, and prolonged exposure to the element for Kryptonians is fatal. Kryptonite's effects is radioactive in nature and therefore cannot penetrate the element lead. The radiation of the mineral can be harnessed and used independent of the mineral itself to harm a Kryptonian, usually appearing in the form of artificial light emitted from certain machinery. Alex taught Kara to fight in a room lined with low-intensity Kryptonite emitters, just enough to be brought down to normal strength. Alex Danvers utilized a sword made from Kryptonite, and it was ultimately used to kill Astra. Physical signs of being affected by Kryptonite are somewhat fever-like, including nausea, weakness, dizziness, vertigo, fatigue, pain, and loss (or near loss) of consciousness. It has even been used as anesthesia or a sedative against Khryptonians do its affects. Kryptonite inside the body causes green glowing veins to protrude from the skin of the Kryptonian and the physical pain it causes becomes unbearable at that point.

Blue Kryptonite
A blue form of kryptonite was created by the D.E.O. by altering the ionic charge of green kryptonite. It was used to subdue Bizarro. While it had no effect on Kryptonians, it severely weakened Bizarro and sedated her, allowing her to be captured and then put in a coma. It also seemed to have a calming effect on her, removing her rage toward Supergirl, causing her to accept the need to put her in a coma and ask for forgiveness for her actions. Therefore, it effectively made her more rational and understanding towards others, something she struggled with before.

Red Kryptonite
Maxwell Lord created a synthetic red form in hopes of subduing Non's next attack. Rather than weaken a Kryptonian physically, Red Kryptonite alters his or her mind. It weakens and gradually destroys the inhibitions of a good Kryptonian. They can even feel its effects long after they have left its presence. As this happens, red glowing veins momentarily protrude from the skin when they first come near it and in times when the victim's actions and thoughts are most affected by the Red Kryptonite. Eventually, the Kryptonian will be left without morality, rationality, or any cares whatsoever. Left with only malice, pride and wrath, the Kryptonian will become malevolent and prone to hostility and aggression, leaving them a danger to everyone around them. However, Maxwell also developed a cure for it in the form of an red energy beam gun that neutralized the red kryptonite at a targeted victim and knocked them out.

Users

 * D.E.O.: Kryptonite is used by the members of the D.E.O., who utilize it against those that hail from the planet Krypton. They utilized it in restraints and certain weapons, such as blades, darts and bullets. Prison cells designed for Kryptonians, as well as training rooms, have kryptonite lights that can be lowered to simply depower a Kryptonian, while higher levels can incapacitate, cripple, and nearly kill them.
 * Maxwell Lord: He created Red Kryptonite in hopes of stopping Non's army. Unfortunately, Kara inadvertently came in contact with it. The Red Kryptonite lowered and gradually destroyed her inhibitions.