The reason why there are so many anonymous groups is so that the addict can identify, e.g. Cocaine Anonymous - I went to one of their meetings because a friend invited me and they pretty much believe that Cocaine is a drug in itself i.e. Nothing like heroin, marihuana etc.
A cross addict using drugs and alcohol will be able to relate to you as much as in Overeaters Anonymous a cross addict using drugs and suffering from bulimia will be able to relate to you, however any pure alcoholic, overeater, gambler, sex addict will not be able to relate to you or your drug use because they have never done it.
NA is a good bet for a drug addict; AA and NA for an alcoholic drug addict; AA, NA, GA for an alcoholic drug addict gambler etc etc.