Red Kryptonite is a radioactive element from Superman's home planet of Krypton.
The kryptonite brings out the rebellious and immoral personality of Kryptonians and rids them of their inhibitions. The effects of red kryptonite are likened to that of being under the influence of too much alcohol or narcotics, without the loss of physical capability.
- Future Lex Luthor uses Red Kryptonite to alter baby Kal-El's personality to assist Lex Luthor in the Brothers in Arms reality. The reality's Lex Luthor keeps a sample of Red Kryptonite in his office.
- The effect red kryptonite has in DC Universe Online first appeared in the Smallville television series.