I think I remember as a kid seeing an episode of a superman cartoon where the red kryptonite made him grow old. Does that ring a bell to anyone?
"No two chunks of red kryptonite have the same effect. Effects are typically depicted to last for 24-48 hours, after which the Kryptonian in question is always immune to that specific chunk of red kryptonite.
Pre-Crisis red kryptonite is created from green kryptonite that passed through a mysterious red-hued cloud en route to Earth. In post-Crisis continuity, red kryptonite first appears as an artificial construct of Mr. Mxyzptlk, then as a synthetic variant created by Ra's al Ghul, using notes stolen from Batman.
Superman has suffered the following random effects upon exposure to various pieces of red kryptonite: being turned into a dragon, a non-powered giant, a dwarf, an ant-headed humanoid, a lunatic, and an amnesiac; being made unable to see anything colored green; growing incredibly long hair, nails, and beard; being rendered totally powerless; growing fat; gaining the ability to read thoughts; growing a third eye in the back of his head; losing his invulnerability along the left side of his body; being split into an evil Superman and a good Clark Kent; being split into young and old forms (Superboy and Superman); being rendered unable to speak or write anything but Kryptonese; growing an extra set of arms; becoming clumsy; swapping bodies with the person nearest him upon exposure to it; transferring his powers; rapidly aging; multiple personality changes; and having his skin rendered transparent, overloading him with solar power.
On the TV series 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. Smallville red kryptonite requires close contact with skin to be effective.
In Krypto the Superdog, effects on Krypto include temporary amnesia, losing all super powers, causing Krypto's tail to detach from his body and come to life, and body-swapping.
In The New Adventures of Superman, Red Kryptonite looked like a big chunk of Kryptonite, rather than a ring or necklace as was in Smallville. It did not have to be in contact with Clark to have an effect - proximity was enough. The effects were slightly different, too - instead of Clark losing his inhibitions, he became apathetic. He simply did not care about catching criminals; instead shrugging his shoulders, blaming others and talking to a girl. It was prophesised 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."
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