There are actually several different types of Kryptonite.
The most famous, Green Kryptonite, will eventually kill a super Kryptonian (e.g. Superman, Supergirl), but it takes a while, usually long enough for a weakened Superhero to say or do something to prevent his death.
Red Kryptonite causes unpredictable but temporary side effects. It is frequently used by the main stream media, sometimes to their detriment (it could, for instance, make a superhero temporaily insane, or temporarily make him 10 feet tall).
Exposure to Gold Kryptonite will remove super powers permanently. The Macaca guy was found with that. There may have been some in the keel of the S.S. Monkey Business as well.
Blue Kryptonite is used only on Bizarro Kryptonians, and is useful against most Democrats.
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Then there was “X” kryptonite that Supergirl created that gave Streaky his super powers, Crystal Kryptonite that Phantom Zone entrapped characters could use to move things in the real world, and anti-kryptonite that could kill a non-super powered krptonian (like in Argo city where Supergirl came from).