Oxycontin is an opiate - one of the most addictive families of drugs. It also happens to have legitimate uses. Those legitimate uses do not negate its potential for abuse. If medical uses for marijuana and cocaine exist, and I believe some do, then I have no problem with their inclusion in the medical tool box - but that does not extend to your desire to spark up a doobie at the Phish concert, or snort/smoke/inject cocaine until you live under a bridge somewhere.
Why do you care so much about what someone else puts into his or her own body of his or her own volition?