Kryptonite

"Made of low-grade Kryptonite. Radioactive mineral from your home planet. It weakens you."

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

Green Kryptonite
"I've never seen anything like it. It's definitely not from this planet. It seems to be emitting a specific radioactivity that's damaging to your cellular structure."

- Astra's associate

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 are 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. Physical contact with Kryptonite of higher intensity is enough to cause burning pain. It has even been used as anesthesia or a sedative against Kryptonians due to 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
The blue, molecular opposite of green kryptonite and was created by the D.E.O. by reversing 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 Kryptonians physically, Red Kryptonite alters their minds by weakening and gradually destroying their inhibitions, as well as bringing out every negative thought to the surface. 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. Symptoms of Red Kryptonite infection first start as the Kryptonian becoming more abrasive and immature in personality and actions as their mental and emotional restraint is lessened. Eventually, the Kryptonian will be left without morality, patience, rationality or any cares, whatsoever. They can even develop narcissistic tendencies and arrogance that results in an inferiority complex. After having expressed their negative personality traits fully, 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 a red energy beam gun that neutralized the Red Kryptonite at a targeted victim and knocked them out, as the Red Kryptonite left the body in the form of red gas.

Silver Kryptonite
A silver colored form of Kryptonite that was found and used by Queen Rhea from the vast quantities of Kryptonite that rained down on planet Daxam. This kryptonite will cause a Kryptonian to fall in a deep and frightful hallucination where nothing from the outside world will stir them out of it until it leaves their system. When Superman confronted Rhea, she poisoned him with it and he was convinced that Supergirl was actually his greatest enemy Zod who had come back to destroy everything he loved. Unlike green kryptonite, silver kryptonite will not weaken or dampen a Kryptonian's powers at all. When in vast quantities, it will reveal itself as glowing silver veins on the Kryptonian's skin.

Synthetic Kryptonite
Due to J'onn J'onzz gave all of the D.E.O.'s remaining green kryptonite to Clark Kent (under the guise of Superman) to keep it hidden or to destroy it preventing Cadmus from further using green kryptonite against Clark and Kara Danvers; Cadmus was forced to create their own synthetic version of kryptonite, although this synthetic kryptonite has the same effects of as green kryptonite as well as serving as the source of Metallo's powers; it was proven to be too unstable, as it eventually exploded, killing Metallo in the process.

Known users

 * Maxwell Lord: Max 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 and turned her into a corrupt version of herself.
 * Rhea: Rhea had Kryptonite weapons forged from the massive amounts of Kryptonite that rained down on Daxam after Krypton was destroyed and ravaged her home world. She later used another form of Kryptonite, Silver, on Superman to make him hallucinate and fight Supergirl.
 * Oliver Queen: Oliver possesses arrows with tips made out of Green Kryponite on the chance that an evil Supergirl would show up.

Former users

 * D.E.O.: Green Kryptonite was used by the members of the D.E.O., who utilize it against those that hail from the planet Krypton. They utilize it in the form of restraints and certain weapons, such as blades, darts and bullets. Prison cells designed for Green Kryptonians, as well as training rooms, have kryptonite lights that can be lowered to simply depower a Green Kryptonian, while higher levels can incapacitate, cripple, and nearly kill them. However, after it was discovered that the D.E.O. had a spy from Project Cadmus who stole the Green Kryptonite from their organization; J'onn J'onzz gave all of the D.E.O.'s remaining green kryptonite to Clark Kent (under the guise of Superman). Whether he destroyed it or kept it hidden is unknown, but based on Kara's comment about how Cadmus still had Kryptonite even though all known kryptonite was with Clark, it was assumed he kept it in the event another Kryptonian posed a threat to earth. However, it was later discovered that the kryptonite Cadmus used, was with in fact synthetic kryptonite.
 * Project Cadmus: Cadmus created a synthetic version of the Green Kryptonite that had the same effects as natural green kryptonite. It was used to power their Green Kryptonite-powered cyborg Metallo. However, the synthetic version proved too unstable and eventually exploded. They also used natural green kryptonite, that was used to power their second green kryptonite-powered cyborg Metallo, however, once the D.E.O. discovered that they had a spy from Cadmus in the organization; J'onn J'onzz gave all of the D.E.O.'s remaining green kryptonite to Clark Kent (under the guise of Superman) to keep it hidden from Cadmus or to destroy it; preventing Cadmus from further using green kryptonite against Clark and Kara Danvers.

Supergirl
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Comics
In the DC comics, there are several different types of Kryptonite:
 * Green Kryptonite: Green Kryptonite can weaken a Kryptonian's physical attributes, however, the radiation effects of green kryptonite are harmful to humans given sufficient long-term exposure, resulting in cancer.
 * Red Kryptonite: Like Green Kryptonite, Red Kryptonite can weaken a Kryptonian's physical attributes; but to a greater degree.
 * Anti-Kryptonite: Anti-Kryptonite is harmless to Kryptonians; but has the same effect as the green variety on normal humans.
 * X-Kryptonite: X-Kryptonite is harmless to Kryptonians; but it gives normal life-forms superhuman powers.
 * Blue Kryptonite: Blue Kryptonite can affect Bizarro in the same way the green variety of kryptonite affects Kryptonians; blue kryptonite is the antidote to the random and bizarre effects of red kryptonite. Generally it is harmless to real Kryptonians. In some fiction, however, it can strengthen the normal physiology of Kryptonians or even heal their wounds.
 * White Kryptonite: White Kryptonite can kill all plant life, from any world.
 * Red-Green Kryptonite: Red-Green Kryptonite caused Superman to mutate, temporarily growing a third eye in the back of his head.
 * Gold Kryptonite: Gold Kryptonite can remove Kryptonians' powers to process yellow sunlight; this kryptonite only removes a kryptonian's powers temporarily, but enough exposure can render them powerless forever.
 * Red-Green-Blue-Gold Kryptonite: Red-Green-Blue-Gold Kryptonite can enhance the intelligence of a Kryptonian.
 * Silver Kryptonite: Silver Kryptonite can causes Kryptonians to suffer from altered perceptions, loss of inhibition and extreme hunger cravings.
 * Jewel Kryptonite: Jewel Kryptonite allows the individual(s) to project illusions or perform mind control.
 * Bizarro-Red Kryptonite: Bizarro-Red Kryptonite affects normal humans the same manner that red kryptonite affects Kryptonians.
 * Red-Green Kryptonite: Red-Green Kryptonite caused Superboy to permanently lose his powers.
 * Red-Gold Kryptonite: Red-Gold Kryptonite temporarily deprives Kryptonians of their memories.
 * Magno-Kryptonite: Magno-Kryptonite is magnetically attracted to all substances originally from Krypton.
 * Red-Green-Gold Kryptonite: Red-Green-Gold Kryptonite can permanently remove the individual's powers and memories of ever having been Superman.
 * Slow Kryptonite: Slow Kryptonite affects normal humans in a manner similar to green kryptonite.
 * Kryptonite-X: Kryptonite-X can supercharge a Kryptonian and restore his/her ability to process solar radiation.
 * Pink Kryptonite: Pink Kryptonite turns Kryptonians lesbian, gay, bisexual or transgender.
 * Black Kryptonite: Black Kryptonite can split a Kryptonian into two separate entities; one good and the other evil.
 * Orange Kryptonite: Orange Kryptonite gives super power to any animal that comes into contact with it for 24 hours.
 * Periwinkle Kryptonite: Periwinkle Kryptonite causes Kryptonians to lose all inhibitions.

Live-action
In live-action media, the most common form of kryptonite seen is green kryptonite. The effects are generally the same in all live-action versions. It weakens a Kryptonian's physical attributes, including blocking the ability of the body's cells to absorb and use yellow solar radiation with continued exposure. Green K can kill with prolonged exposure.

Other types of kryptonite have also appeared.

In Superman III: On The Adventures of Superboy: On Lois & Clark: The New Adventures of Superman: In Superman Returns: On Smallville:
 * Synthetic Kryptonite: Artificially created kryptonite that substitutes cigarette "tar" in place of an unknown component of true kryptonite. Intended to harm and kill Superman, the flawed kryponite initially corrupts Superman, then splits him into two personas: a belligerent, selfish, and careless Superman; and good, kindhearted, mild-mannered Clark Kent. The two fight and when Clark wins, the personas merge and Superman returns to normal.
 * Red Kryptonite: Man-made form of kryptonite created while trying to neutralize the effects of green kryptonite so it could be used as an alternative power source. Superboy turned evil with a single exposure; a second exposure reversed the effects.
 * White Kryptonite: Unlike its comic counterpart, white kryptonite was created by using the same duplicating ray that made Bizarro in an attempt to form a kryptonite to kill Bizarro. Instead, the white K stabilized and cured the molecularly unstable Bizarro.
 * Red Kryptonite: Clark Kent was shown to suffer differing effects when exposed to red K at different times, including apathy, uncontrollable increase of his powers, and a transfer of his powers to Lois Lane.
 * "Hybrid" Kryptonite: A man-made form created by a renegade S.T.A.R. Labs scientist. Harmless to Kryptonians; caused the same effect on humans as green kryptonite on Kryptonians.
 * Green Kryptonite: Lex Luthor combined green K with Kryptonian crystalline technology to create a new continent off the coast of Metropolis that threatened to destroy North America.
 * Green Kryptonite: Also caused mutations in humans, animals, and plants. Humans developed a variety of superhuman abilities that typically proved dangerous to themselves and others. In some cases, the radioactivity of green K could be neutralized and the resulting "clear" kryptonite would be harmless to Kryptonians and humans.
 * Red Kryptonite: Continuous contact with red K compromised Clark Kent's inhibitions and morality, often causing him to break the law and act selfish and rebellious. Similarly, Clark's friends Chloe Sullivan and Pete Ross became adrenaline addicts with little regard for others. Red K-infused lipstick caused a similar reaction in Lois while also bringing up a passionate attraction to Clark. Removing the contact quickly ended the effects.
 * Black Kryptonite: Could separate aspects of the psyche of Kryptonians or humans and manifest them in a duplicate body, typically as "good" and "bad" versions of someone. Black K was created by superheating green kryptonite to extremely high temperatures.
 * Silver Kryptonite: An artificial kryptonite infused with silver shards created by the liquid metallic form of Brainiac. The silver induced hallucinations and paranoia in Kryptonians. It also suppressed their general invulnerability, allowing them to be cut so the silver could enter the bloodstream.
 * Blue Kryptonite: Suppressed superhuman abilities in Kryptonians with continuous contact, specifically resistance to illness and injury. Aging in Kryptonians was also increased to the speed of humans by prolonged contact. Kryptonians were resistant to effects of green kryptonite when in contact with blue K. In humans, blue K dramatically improved health. With Bizarro, blue K exponentially increased the clone's powers to the point the body became unstable and exploded, killing the Phantom Zone wraith.
 * Gemstone Kryptonite: A mineral infused with kryptonite that would give Kryptonians the power of hypnotic persuasion over others. It was primarily seen in pulverized dust form. The persuasion could also affect the Kryptonian persuader if their command was directed back at them through a reflective surface. The effects were counteracted with green K.
 * Gold Kryptonite: Exposure suppressed Kryptonian invulnerability, allowing wounds and permanent scarring. Direct contact could permanently remove all Kryptonian superhuman abilities. Contact with a large amount or prolonged contact with gold K could kill a Kryptonian.