||As a stimulant, cocaine would just as likely make a difficult LSD trip worse. The increase in pulse and blood pressure would likely cause anxiety. Cocaine itself often causes anxiety and paranoia. It may redirect the experience, but I don't think it would be in a positive direction.|
Traditionally, when a person is having a rough trip, hospitals give either anti-psychotics such as haloperidol, Risperdal, and Thorazine, or anti-anxiety drugs such as Valium or Xanax. The anti-psychotics are more geared towards ending a trip while the anxiolytics are intended to redirect the experience by reducing the anxiety. Individuals without access to these substances sometimes choose to use mild depressants such as Kava, Alcohol, or GHB.
More information about 'antidotes' can be found in the appendix of the Psychedelic Crisis FAQ.
It's good to remember that many people believe the best remedy for a bad trip is an understanding friend and a little time.