Propoxyphene is chemically related to Methadone. the brand name for it is DARVON. It's weak as hell. Weaker than codeine even. And it has very bad effects on the liver and it can send you into a psychotic rage. Not many doctors use it for pain cuz of the bad effects. Just use codeine instead. Propoxyphene is also related to demerol, another horrible drug with bad effects.