The drug songs seem to keep cropping up. See the Ain't Nobody's Business thread for some cocaine songs. There was a recent thread on Buffy Sainte Marie's song Codeine. Another recent thread covered Tom Paxton's Talking Vietnam Pot Luck.
Too many flower children perhaps?
Anybody remember a guy named Jim Post? He had a wonderful tune about LSD called Brain Damage.
Alcohol for many localities and in many times was the only serious drug of choice. Hence, there are more songs about alcohol. During the rag-time era, cocaine and marijuana became the subject of some songs. Off the top of my head, I don't recall many references to heroin or morphine
A search of the DT provides little on heroin and morphine. There are multiple songs that mention drugs, but only a few that focus intently on them.
Roger in Baltimore