1.   Methadone, a synthetic drug developed as a painkiller in World War II, was subsequently discovered to block opiate cravings.

2.   Methadone, for example, blocks the craving for heroin, but only heroin.

3.   Revia, which is not an aversive agent, blocks the craving for alcohol and the euphoric feeling of getting high.

4.   Generically known as naltrexone, it blocks the craving for the drug and the heady feeling of getting high.