See the main article on Kryptonite here.

Pre-Crisis

Red kryptonite was the result of a shower of regular green kryptonite from the destruction of Krypton passing through a strange, red-hued cosmic cloud. The debris that made it to Earth provoked effects on Superman that were never replicated, as he gained an "immunity" from that effect. The effects of red kryptonite are temporary and last up to 72 hours.

Some of the documented effects from this era include:

• Mental telepathy.
• Uncontrollable hair and nail growth.
• Transformation into a Kryptonian monster known as Drang.
• Temporary insanity.
• It was swallowed by the Kryptonian Flame-Dragon but caused no effects on the Flame-Dragon or Superman. (Superman #142)
• It created a good and evil Superboy. (Adventure Comics #255)
• It turned Superboy's figure into three different forms: fat, tiny and giant. (Adventure Comics #270)
• It turned Superboy into three odd characters: a lion boy, a human magnet and Jesse James. (Superboy #103)
• It made Superboy reveal his secret identity. (Superboy #107)
• It paralyzed Superboy. (Superboy #85)
• It caused Superboy to grow an extra finger on each hand. (Superboy #105)
• It caused Superboy speechlessness. (Adventure Comics #307)
• It caused Superboy amnesia. (Adventure Comics #268 & #284)
• It restored Superboy's power after being under the effects of a Red Sun. (Superboy #81)

Post-Crisis

Mister Mxyzptlk creates what he calls red kryptonite in the "Krisis of the Krimson Kryptonite" story arc but it has no radioactive properties at all; Superman's depowering is all the result of Mxyzptlk's magic until Luthor unknowingly breaks the rules of his agreement with Mxyzptlk. The first appearance of actual red kryptonite is as a synthetic variant created by Ra's al Ghul, using notes stolen from Batman. This version of the Red Kryptonite causes Superman intense pain (but not to the lethal levels of Green Kryptonite) as well as his powers to behave oddly and his skin to become transparent. Later, a piece of Red Kryptonite found by Ambush Bug and brought to the Fortress of Solitude caused him and Superman to switch their bodies for 48 hours. In The Brave and the Bold series, the cloud was drawn to Earth by the deranged alchemist Megistus to shield humanity against the effects of the Final Crisis by warping it into something totally different; the villain Doctor Alchemy also proved capable of transmuting the Fortress of Solitude in its entirety into red kryptonite using his philosopher's stone.

In Other Media

Lois & Clark: The New Adventures of Superman

Red kryptonite initially caused Superman to become apathetic. It was hypothesized that, given enough exposure to red kryptonite, Clark's condition would become permanent. However, after talking to a psychiatrist, Clark was able to resist the effects of the red kryptonite, and he picked up the rock and threw it out of a window. Its later appearances included a red kryptonite laser which caused Superman's powers to transfer to Lois, and exposure causing Superman's powers to be increased beyond his ability to control them.

Smallville

Red kryptonite has a drug-like effect, causing severe changes in Clark Kent's personality. Under this influence, Clark loses his inhibitions, becoming unpredictable and acting purely on erotic and selfish emotions. Once he ran away to Metropolis and became a criminal who broke into automated-teller machines to impress girls with expensive toys such as sports cars. He also stole his father's credit card to buy large screen TVs and high end audio equipment.

Smallville

Red kryptonite requires close contact with skin to be effective, such as being worn in a ring or necklace.

Krypto the Superdog

Effects on Krypto include:

• Temporary amnesia.
• Loss of all his super-canine powers.
• Causing Krypto's tail to detach from his body and come to life.
• Turning into a fish.
• Body-swapping.