Green’s Dictionary of Slang

(US campus) a habitual drinker or drug user.

1979		T. Alibrandi Custody 61: He’s a loadie, and he’ll want to score.
1986		J. Ellroy Suicide Hill 10: The other mechanics were loadies who were always ragging him about his disdain for dope.
1995		A. Heckerling Clueless [film script] tai: Thanks. Wow, a party! cher: It’s in the Valley. The cops usually break ’em up in less than an hour, and it takes that long to get there. dionne: And besides, it’s just local loadies.