New medicines to combat addiction to drugs like heroin and Oxycontin are in the works. The drugs block the high that abusers feel.

Herbert Kleber, professor of psychiatry at Columbia University in New York City, says researchers are experimenting with an injectable version of naltrexone, already used to treat narcotic addiction. One dose interrupts the effects of heroin for up to four weeks. Researchers hope testing will begin soon on an implantable version already in use in Australia that could last for as many as 12 months. Daily addiction medications have always been problematic because patients don't take them, says Kleber.

Would addicts need to take the drugs for life? Kleber says that isn't yet clear, but that the medications shouldn't be seen by doctors as a substitute for rehabilitation therapy.