1) Term for a drug user. Possibly originating from the manner in which
solvent addicts
imbibe glue; they put the substance into a bag then repeatedly breath in and out with the bag over their mouth.
2) Its modern use is more likely to refer to a smack (heroin) addict and is usually a term of abuse.
1)
That bag head was in my shop buying glue again today.
2) Some
dirty bag heads left
needles on the school playing field.